HIGH-MOLECULAR-WEIGHT NOVOLAK SUBSTITUTED PHENOLIC RESINS AND THEIR PREPARATION

Abstract: Conventional novolak phenolic resins generally possess molecular weights of 1200 or less and exhibit unsatisfactory heat resistance and mechanical properties for all intended uses. Attempts to produce higher-molecular-weight resins have failed. These difficulties have been overcome and a high-molecular-weight novolak substituted phenolic resin having a number average molecular weight of at least 1500 is prepared by reacting (A) (i) a phenol component mainly com­ prising a bifunctional phenol or (ii) a low-molecular-weight novolak substituted phenolic resin derived from this phenol and an aldehyde, with (B) a chain extender selected from (i) dimethylolated products of bifunctional or trifunctional phenols, (ii) a low-molecular-weight resol substituted phenolic resin derived from a phenol component mainly comprising a bifunctional phenol and an aldehyde, (iii), an aldehyde, (iv) a ketone, (v) a diol and (vi) a dihalide in the presence of an acid catalyst, with the proviso that if the reac­ tant (A) is the phenol component (i), the chain extender (B), is the resol substituted pnenolic resin (ii). These high-­ molecular-weight novolak resins can be used in setting resin compositions with setting resins such as epoxy resins.

Description: The present invention relates to a process for the preparation of a high-molecular-weight novolak substituted phenolic resin and to such a resin. Ordinarily, novolak phenolic resins are prepared by condensing a phenol with an aldehyde in the presence of an acid catalyst, and it is known that the obtained resins have a structure in which phenol units are connected through methylene groups bonded at the 2,6- or 2,4-positions thereof and in which methylol groups are not present or, if present, the amounts of methylol groups are very small. Novolak phenolic resins prepared according to this known process ordinarily have a number average molecular weight of 250 to 800. The number average molecular weight is about 1000 at the highest. The melting point of these novolak phenolic resins is low. Furthermore, it is known that a novolak substituted phenolic resin having a structure similar to that above is obtained by condensing a substituted phenol having an alkyl group or halogen atom at the para- or ortho- position of the phenol nucleus with an aldehyde in the presence of an acid catalyst. However, the number average molecular weight of this phenolic resin is similarly low and ordinarily in the range of from 250 to 800, and is 1200 at highest. Accordingly, the melting point of this phenolic resin is low too. Therefore, even if this novolak resin is combined with other setting resins, optionally also with a filler or additive, and the resulting compositions are cured, there cannot be obtained cured resin compositions possessing excellent heat resistance and mechanical properties. As is seen from the above description, the number average molecular weight of novolak phenol-formaldehyde resins prepared according to conventional processes is very low and is ordinarily in the range of from 250 to 800 and is 1200 at highest. It was reported that when such a novolak phenol-formaldehyde resin is fractionated, a novolak phenol-formaldehyde resin having a molecular weight of about 3000 to about 10000 is obtained though the yield is very low [see Lectures on Plastic Materials, Volume 15, Phenolic Resins, pages 14―24, written by Shinichi Murayama and published by Nikkan Kogye Shinbunsha and J. J. Gardikes and F. M. Konrad, Am. Chem. Soc., Div. Org. Coating and Plastics Chemistry, 26 , No. 1, 131―137 (1966)]. However, since the high-molecular-weight novolak phenol-formaldehyde resin obtained by fractionation has a narrow molecular weight distribution and since a gelation product is readily formed by partial crosslinking owing to the trifunctional characteristic of the phenol and is contained in the obtained resin, even if such a phenolic resin is incorporated in a setting resin, it is impossible to sufficiently improve the heat resistance and mechanical properties of the resulting resin composition. Furthermore, the process for preparing such high-molecular-weight novolak phenol-aldehyde resins disclosed in the above references, that is fractionating a novolak phenol-formaldehyde resin having a low number average molecular weight to obtain a high-molecular-weight novolak phenol-formaldehyde resin in minute yields, is not advantageous from the industrial viewpoint. Attempts have been made to obtain a high-molecular-weight novolak substituted phenolic resin by polycondensing a bifunctional alkyl phenol such as an o-alkyl or p-alkyl phenol with an aldehyde in the presence of an acid catalyst. However, the number average molecular weight of the obtained novolak alkyl-substituted phenolic resin is only up to 1200. A novolak alkyl-substituted phenolic resin having a sufficiently high number average molecular weight has not been obtained [see, for example, F. S. Granger, Industrial and Engineering Chemistry, 29 , 860―866 (1937), J. B. Nierderl and I. W. Ruderman, Journal of American Chemical Society, 67 , pages 1176―1177 (1945), and R. F. Hunter and V. Vand, Journal of Applied Chemistry (London), 1 , page 298 (1951)]. Novolak alkyl-substituted phenolic resins have a low number average molecular weight and a low melting point, though they have a chain-like or linear structure. Also attempts have been made to obtain a high-molecular-weight novolak chlorophenol resin by polycondensing p-chlorophenol or o-chlorophenol with formaldehyde in the presence of an acid catalyst. For example, W. J. Burke and S. H. Ruteman et al , Journal of Polymer Science, 20 , 75―88 (1956) disclose a high-molecular-weight novolak chlorophenol resin having a number average molecular weight higher 1600 or 3300 obtained by polycondensing p-chlorophenol with formaldehyde, W. J. Burke and S. H. Ruteman, Journal of Polymer Science, 32 , pages 221―228 (1958) disclose a high-molecular-weight novolak chlorophenol resin having a number average molecular weight higher 1610 or 3640 obtained by similarly polycondensing p-chlorophenol with formaldehyde and acetylating the resulting reaction product. However, these high-molecular-weight novolak chlorophenol resins have been denied by researches made afterwards. It has been proved that the acetylation product is a low-molecular weight novolak chlorophenol resin having a number average molecular weight lower than 1250 [Minoru Imoto and Keikichi Uno, Lectures on Polymerization Reactions, Volume 8, Polyaddition and Addition Condensation (published by Kagaku Dojin) and Minoru Imoto and Shinichi Nakade, Bulletin of Chemical Society of Japan, 36 , pages 580―585 (1963)]. In short, novolak chlorophenol resins disclosed in these prior art references have a low number average molecular weight and a low melting point though they have a chain-like or linear molecular structure. Even if these novolak chlorophenol resins are incorporated in setting resins to form resin compositions, it is impossible to sufficiently improve the heat resistance and mechanical properties. Japanese Patent Application Laid-Open Specification No. 116081/79 teaches that when a phenol and an aldehyde are subjected to addition condensation in the presence of an acid catalyst and a Lewis acid is added to effect removal of the phenol at an appropriate time during a period of from the point before completion of the reaction to the point after removal of condensed water, a linear novolak phenolic resin free of a three-dimensional cross-linked structure (gelation product) is obtained. In the Examples of this Japanese Specification, the only phenol used is phenol itself. However, in the text of the Japanese Specification, it is taught that not only phenol but also alkyl phenols such as cresol and p-tert-butylphenyl can be used as the phenol. We effected the tracing experiments of the Examples of this Japanese Specification, and found that each of the novolak phenol-formaldehyde resins obtained contains a considerable amount of a three-dimensional crosslinked structure (gelation product) and that the number average molecular weight of the residue left after removal of the gelation product is in the range of from about 500 to about 1100. This residue is a low-molecular-weight novolak phenolic resin (see Comparative Example 4 given hereinafter). It has now been found that if a phenol component mainly comprising a bifunctional phenol is reacted with a resol phenolic resin derived from a phenol component mainly comprising a bifunctional phenol and an aldehyde in the presence of an acid catalyst, or if a novolak phenolic resin derived from a phenol component mainly comprising a bifunctional phenol and an aldehyde, is reacted with a chain extender such as a dimethylolated product of a phenol, a resol phenolic resin, an aldehyde, a ketone, a diol or a dihalide in the presence of an acid catalyst, a substantially linear, high-molecular-weight novolak phenolic resin having a number average molecular weight of from 1700 to 15000 is obtained. Accordingly, the present invention provides a process for the preparation of a high-molecular-weight novolak phenolic resin wherein (A) (i) a phenol component mainly comprising at least one bifunctional phenol represented by the general formula [I]: wherein two of the three R¹′s are hydrogen atoms and the remaining R¹ is an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen atom or a hydroxyl group, and the two R′s, which may be the same or different, represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a halogen atom or a hydroxyl group, wherein the R¹ group which is not a hydrogen atom is in the para position with respect to the hydroxy group, or (ii) a novolak phenolic resin derived from a phenol component mainly comprising said bifunctional phenol of general formula [I] and an aldehyde represented by the general formula: R²―CHO [II] wherein R² represents a hydrogen atom, a methyl group or a halogenated methyl group, and having a number average molecular weight of from 250 to 1200, is reacted with (B) a chain extender selected from (i) dimethylolated bifunctional and trifunctional phenols, (ii) resol phenolic resins derived from a phenol component mainly comprising said bifunctional phenol of general formula [I] and said aldehyde of general formula [II] and having a number average molecular weight of from 250 to 1200, (iii) aldehydes, (iv) ketones, (v) diols and (vi) dihalides, with the proviso that when reactant (A) is the phenol component (i), the chain extender (B) is the resol phenolic resin (ii), in a solvent in the presence of an acid catalyst, so that at least 70 mole % of the phenol component in the final novolak phenolic resin is derived from said bifunctional phenol of general formula [I], until the number average molecular weight of the final novolak phenolic resin is from 1700 to 15000 as measured by vapour pressure osmometry in N,N-dimethylacetamide as solvent, the ratio M w/ M n of the weight average molecular weight to the number average molecular weight is from 1.8 to 20 and the melting point of said resin is higher than 160°C. The present invention also provides a substantially linear, high-molecular-weight novolak phenolic resin which comprises substantially linear novolak recurring units (a) formed by condensation of a phenol component comprising at least 70 mole % of at least one bifunctional phenol represented by the general formula [I] as defined above with at least one aldehyde represented by the general formula [II] as defined above, said resin having a number average molecular weight of from 1700 to 15000 as measured by vapour pressure osmometry in N,N-dimethylacetamide as solvent the ratio M w/ M n of the weight average molecular weight to the number average molecular weight is from 1.8 to 20 and the melting point of said resin is higher than 160°C. This resin may contain intervening groups (b) consisting of a divalent hydrocarbon group, which appear between blocks of the novolak recurring units having a number average molecular weight of 250 to 1200, in an amount of 0.5 to 1 mole per mole of said blocks. The high-molecular-weight novolak phenolic resin (hereinafter referred to as a "high-molecular-weight novolak resin") according to the present invention may comprise novolak recurring units, all of which are substantially linear. Alternatively it may contain intervening or bridging groups consisting of a divalent hydrocarbon group, which appear alternately in between blocks of the novolak recurring units having a number average molecular weight of 250 to 1200, in an amount of 0.5 to 1 mole per mole of said blocks. What is important is that the high-molecular-weight novolak resin is substantially linear and has a number average molecular weight of from 1700 to 15000. By the term "substantially linear" is meant that the molecular structure of the polymer is a linear structure including straight or branched chains but is substantially free of crosslinkages (gelled portions). The number average molecular weight of the substantially linear high-molecular-weight novolak resin is determined according to vapour pressure osmometry in N,N-dimethylacetamide as solvent. The number average molecular weight must be from 1,700 to 15,000 and when the resin is used as an additive to a setting resin, the heat resistance and mechanical properties are improved. These effects are especially enhanced if the number average molecular weight of the high-molecular-weight novolak resin is in the range of from 2,000 to 10,000. As pointed out above, the high-molecular-weight novolak resin must have a number average molecular weight of from 1700 to 15000. In general, a higher number average molecular weight is preferred, because the heat resistance and mechanical properties of the composition formed by incorporating this resin into a setting resin are improved as the number average molecular weight of the resin is increased. The molecular weight distribution of the high-molecular-weight novolak resin is such that the content of resin components having a number average molecular weight of at least 2,000 is ordinarily at least 50% by weight, preferably at least 60% by weight and especially preferably at least 70% by weight. The molecular weight distribution expressed as the ratio M w/ M n is in the range of from 1.8 to 20 and preferably in the range of from 2 to 10. The melting point of the high-molecular-weight novolak resin is higher than 160°C. In the bifunctional phenol of the general formula [I], the R¹ which is not a hydrogen atom is preferably an alkyl group having 1 to 8 carbon atoms, and is especially a methyl, ethyl, isopropyl, sec-butyl, tert-butyl or octyl group. A methyl group is most preferred. In the general formula [I], one of two R groups is preferably a hydrogen atom and the other R group is preferably a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and it is especially preferred that each R group is a hydrogen atom. The phenol forming the novolak recurring units comprises 70 to 100 mole %, preferably 80 to 100 mole %, especially preferably 90 to 100 mole %, of at least one bifunctional phenol represented by the general formula [I] and up to 30 mole %, preferably up to 20 mole %, especially preferably up to 10 mole %, of a trifunctional phenol. The total amount of both the phenols is 100 mole %. In the aldehyde of the general formula [II], the group R² is preferably a hydrogen atom or a methyl group and is especially preferably a hydrogen atom. In the novolak recurring units, the bifunctional phenol represented by the general formula [I] is present in the polymer chain in the form of hydroxyarylene units represented by the general formula [IV]: wherein R¹ and R are as defined above. The bifunctional phenol is present at the terminals of the polymer chain in the form of hydroxyaryl units represented by the general formula [V]: wherein R¹ and R are as defined above. The trifunctional phenol of the resin is present in the polymer molecule chain in the form of hydroxyarylene units similar to those represented by the general formula [IV] and is present at the terminals of the resin molecule in the form of hydroxyaryl units similar to those represented by the general formula [V]. In the high-molecular-weight novolak resin of the present invention, the aldehyde represented by the general formula [II] is present in the novolak recurring units in the form of alkylidene units represented by the general formula [VI]: wherein R² is as defined above. The novolak recurring units (a) constituting the high-molecular-weight novolak resin of the present invention form a substantially linear chain structure in which the above-mentioned hydroxyarylene units and alkylidene units are alternately arranged and connected with one another. More specifically, the structure of the novolak recurring units (a) constituting the high-molecular-weight novolak resin of the present invention is such that when the phenol is comprised solely of the bifunctional phenol represented by the general formula [I], the resin is linear and if the content of the trifunctional phenol is increased, the resin sometimes has a branched structure. The ratio of the aldehyde component to the total phenol component in the novolak recurring units is such that the amount of the aldehyde component is ordinarily in the range of from 0.90 to 1.0 mole, preferably from 0.93 to 1.0 mole, per mole of the total phenol component. Ordinarily, the novolak recurring units (a) are free of methylol groups, but they may comprise such group in a minute amount, for example up to 0.01 mole per mole of the total phenol component. The bifunctional phenol represented by the general formula [I] has on the benzene nucleus two hydrogen atoms active to the substitution reaction. In other words the two ortho-positions with respect to the phenolic hydroxyl group are occupied by hydrogen atoms. The bifunctional phenol of the general formula [I] has an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen atom or a hydroxyl group at one of the ortho- or para-positions to the hydroxyl group. For example, there can be mentioned ortho- and para-isomers of alkylphenols such as cresol, ethylphenol, n-propylphenol, isopropylphenol, n-butylphenol, sec-butylphenol, tert-butylphenol, sec-amylphenol, tert-amylphenol, hexylphenol, heptylphenol and octylphenol, halogenated phenols such as fluorophenol, chlorophenol and bromophenol, and arylphenols such as phenylphenol and tolylphenol. Furthermore, the bifunctional phenol represented by the general formula [I], can be 2,3-xylenol, 3,4-xylenol, 2,5-xylenol, 2,3-diethylphenol, 3,4-diethylphenol, 2,5-diethylphenol, 2,3-diisopropylphenol, 3,4-diisopropylphenol, 2,5-diisopropylphenol, 2,3-dichlorophenol, 3,4-dichlorophenol, 2,5-dichlorophenol, 2-methyl-3-phenylphenol, 3-methyl-4-phenylphenol and 2-methyl-5-phenylphenol. The bifunctional phenol component in the novolak recurring units (a) is derived from at least one phenol of general formula [I] and it may be a mixture of two or more of the foregoing phenols. The optional trifunctional phenol is a phenol having on the benzene nucleus three hydrogen atoms active to the substitution reaction. In other words, the two ortho- positions and one para- position with respect to the phenolic hydroxyl group are all occupied by hydrogen atoms. Such trifunctional phenol can be phenol, meta-substituted phenols and 3,5-di-substituted phenols. As substituents which such trifunctional phenol can have at the meta- or 3,5-positions, there can be mentioned alkyl groups, halogen atoms and hydroxyl groups. Trifunctional phenols represented by the general formula [III] are preferred: wherein R, which may be the same or different, stands for a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a halogen atom or a hydroxyl group. As specific examples, there can be mentioned phenol, meta-substituted phenols such as m-cresol, m-ethylphenol, m-n-propylphenol, m-isopropylphenol, m-n-butylphenol, m-sec-butylphenol, m-tert-butylphenol, m-n-amylphenol, m-sec-amylphenol, m-tert-amylphenol, m-hexylphenol, m-heptylphenol, m-octylphenol, m-fluorophenol, m-chlorophenol, m-bromophenol and resorcinol, and 3,5-di-substituted phenols such as 3,5-xylenol, 3,5-diethylphenol, 3,5-diisopropylphenol, 3,5-di-sec-butylphenol, 3,5-di-tert-butylphenol, 3,5-di-sec-amylphenol, 3,5-di-tert-amylphenol, 3,5-dihexylphenol, 3,5-di-heptylphenol, 3,5-dioctylphenol, 3,5-dichlorophenol, 3,5-difluorophenol, 3,5-dibromophenol and 3,5-diiodophenol. Among these trifunctional phenols, those represented by the general formula [III] in which one of the two R groups is a hydrogen atom and the other R group is selected from a hydrogen atom, an alkyl group having 1 to 8 carbon atoms and a chlorine atom are especially preferred. Phenols in which one of the two R groups is a hydrogen atom and the other R group is a hydrogen atom, a methyl group, an isopropyl group, a sec-butyl group, a tert-butyl group or an octyl group are particularly especially preferred. The aldehyde represented by the general formula [II] can be formaldehyde, acetaldehyde, monochloroacetaldehyde, dichloroacetaldehyde or trichloroacetaldehyde. Among these aldehydes, formaldehyde and acetaldehyde, especially formaldehyde, are preferred. The aldehyde is present in the novolak recurring unit block (a) in the form of an alkylidene group represented by the general formula [VI]. In the present invention, the novolak recurring units (a) may be separated by intervening or bridging groups (also called "chain extender component units" hereinafter) consisting of a divalent hydrocarbon group. These chain extender component units appear alternately in between blocks of the novolak recurring units (a) having a number average molecular weight of 250 to 1,200. The resin of this type is characterized in that the novolak recurring unit blocks (a) and the chain extender component units (b) are alternately arranged and connected to one another, whereby the molecular weight of the resin is increased, and that the novolak recurring unit blocks (a) are bonded to terminals of the molecule of the resin. The simplest structure of a resin of this type comprises two molecules of the novolak recurring unit blocks (a) connected to each other through one molecule of the chain extender component unit (b). The next simplest structure comprises 3 molecules of the novolak recurring unit blocks (a) and two molecules of the chain extender component units (b) which are alternately arranged and connected to one another. Furthermore, there can be mentioned a structure comprising 4 molecules of the novolak recurring unit blocks (a) and 3 molecules of the chain extender component units (b) which are similarly alternately arranged and connected to one another, and a structure comprising n molecules of the novolak recurring unit blocks (a) and (n-1) molecules of the chain extender component units (b) which are alternately arranged and connected to one another. The ratio of the units (a) and (b) constituting a resin of this type is such that the amount of the chain extender component units (b) is preferably 0.5 to 1 mole, especially preferably 0.66 to 1.0 mole, per mole of the novolak recurring unit blocks (b). The high-molecular-weight novolak resin of the present invention has a polymer chain diagrammatically represented substantially by the following formula [VII]: wherein Z stands for a substantially linear novolak recurring unit block formed by condensation of the above-mentioned phenol and aldehyde components, Y stands for an intervening group consisting of a divalent hydrocarbon group, p is 0 or 1, and n is zero or an integer of at least 1. In the high-molecular-weight novolak resin containing alternate novolak recurring unit blocks and chain extender component units, p is 1. Group Y can be selected from hydrocarbon groups having 1 to 16 carbon atoms, such as alkylidene groups, alkylene groups, cycloalkylene groups, cycloalkylidene groups, arylalkylidene groups, arylalkylene groups and arylene-bis-alkylene groups [―R³―Ar―R⁴― wherein Ar represents an arylene group and R³ and R⁴, which may be the same or different, represent alkylene groups]. The alkylidene group can be a methylene, ethylidene, propylidene or butylidene group. The alkylene group can be a ethylene, propylene, isopropylene, butylene, pentylene or hexylene group. The cycloalkylene can be a cyclopentylene, cyclohexylene or methylcyclohexylene group. The cycloalkylidene group can be a cyclopentylidene, cyclohexylidene or methylcyclohexylidene group. The arylalkylidene group can be a benzylidene, o-xylidene, m-xylidene or p-xylidene group. The arylalkylene group can be a styrene, α-methylstyrene or p-methylstyrene group. The arylene-bis-alkylene group can be a o-xylylene, m-xylylene or p-xylylene group. Among these chain extender component units (b), alkylidene, alkylene, cycloalkylidene, cycloalkylene, arylalkylidene, arylalkylene and arylene-bis-alkylene groups are preferred. Alkylidene groups having 1 to 4 carbon atoms, alkylene groups having 2 to 5 carbon atoms, arylalkylidene groups having 7 to 9 carbon atoms, arylalkylene groups having 8 to 10 carbon atoms and arylene-bis-alkylene group having 8 to 10 carbon atoms are especially preferred. When the molecular weight of these chain extender component units (b) is too high, the melting point of the resulting high-molecular-weight novolak substituted phenolic resin is reduced but its flexibility is increased. Therefore, if such a resin is combined with a setting resin, resin compositions possessing excellent heat resistance and mechanical properties can hardly be obtained. Accordingly, it is preferred that the molecular weight of the chain extender component unit (b) is 14 to 200, and especially 14 to 170. The structure of the substantially linear high-molecular-weight novolak resin may be determined according to the following methods. The content of units derived from the bifunctional and trifunctional phenols is determined by ¹H nuclear magnetic resonance spectroscopy, ¹³C nuclear magnetic resonance spectroscopy and pyrolysis gas chromatography. By ¹H nuclear magnetic resonance spectroscopy and ¹³C nuclear magnetic resonance spectroscopy, the content of the total phenol component can be obtained from the intensity of the signal based on the hydrogen atom of the phenolic hydroxyl group of the phenol component in the resin, and the ratio of the bifunctional phenol to the trifunctional phenol can be determined from the relation of the intensity of the signal based on the hydrogen atom of the phenolic hydroxyl group to the intensities of the signals of the hydrogen atoms bonded to the benzene nucleus at the ortho-, meta- and para-positions with respect to said phenolic hydroxyl group. The contents of the total phenol component and the aldehyde component in the resin are determined by ¹H nuclear magnetic resonance spectroscopy. The ratio of the bifunctional phenol to the trifunctional phenol can also be determined from the results of pyrolysis gas chromatography. This ratio is calculated on the basis of the results of the determination of phenols formed by pyrolysis. The ratio of methylol groups to methylene groups contained in the resin can be determined from the results of the ¹H nuclear magnetic resonance analysis. The number average molecular weight ( M n) of the high-molecular-weight novolak resin of the present invention is measured by vapour pressure osmometry in N,N-dimethyl-acetamide as solvent. The molecular weight distribution ( M w/ M n) expressed as the ratio of the weight average molecular weight ( M w) to the number average molecular weight ( M n) in the resin of the present invention is determined by gel permeation chromatography using tetrahydrofuran as solvent. The molecular weight distribution expressed as the content of the resin components having a number average molecular weight ( M n) of at least 2,000 is determined from a distribution curve of the number average molecular weights determined according to the above-mentioned method. The melting point of the high-molecular-weight novolak resin is measured by the microscopic method. The temperature at which melt flow is initiated is befined as the melting point. The process for the preparation of a substantially linear high-molecular-weight novolak resin according to the present invention includes the following four embodiments. Embodiment I A low-molecular-weight novolak phenolic resin (c) is reacted with a dimethylolated phenol (d) as a chain extender in the presence of an acid catalyst. In this embodiment, the dimethylolated phenol (d) as the chain extender cannot be distinguished from the novolak recurring unit after it has been included in the molecular chain. Accordingly, in the general formula [VII] representing the product resin, p is zero. The low-molecular-weight novolak phenolic resin (c) used as the starting substance in this embodiment is characterized by the following three features: (A) The phenol component is comprised mainly of at least one bifunctional phenol and is especially a phenol component comprising 70 to 100 mole %, preferably 80 to 100 mole %, especially preferably 90 to 100 mole %, of a bifunctional phenol and up to 30 mole %, preferably up to 20 mole %, especially preferably up to 10 mole %, of a trifunctional phenol. The total amount of both the phenols is 100 mole %. (B) The aldehyde component is at least one aldehyde represented by the general formula [II]. (C) The number average molecular weight of the low-molecular-weight novolak phenolic resin is 250 to 1,200, preferably 350 to 1,000 and especially preferably 400 to 800, as measured according to the vapour pressure osmometry in N,N-dimethylacetamide as solvent. The structure of this starting novolak phenolic resin (c) will now be described. The bifunctional phenol of the phenol component of the novolak phenolic resin (c) is present in the form of hydroxyarylene units represented by the general formula [IV] and in the form of hydroxyaryl units represented by the general formula [V] at terminals of the resin molecule. Also the trifunctional phenol is similarly present in the form of hydroxyarylene units of the general formula [IV] and in the form of hydroxyaryl units of the general formula [V] at terminals of the resin molecule. The aldehyde of general formula [II] of the starting novolak phenolic resin is present in the form of methylene units represented by the general formula [VI]. This starting novolak phenolic resin (c) has a chain structure in which the hydroxyarylene and methylene units are alternately arranged. More specifically, the phenol component is comprised solely of a bifunctional phenol represented by the general formula [II], the novolak substituted phenolic resin is linear. If the content of the trifunctional phenol is increased, the phenolic resin sometimes has a branched chain structure. The ratio of the aldehyde component to the total phenol component in this starting novolak phenolic resin (c) is such that the amount of the aldehyde component is 0.95 to 1.0 mole, preferably 0.97 to 1.0 mole, per mole of the total phenol component. Ordinarily, the novolak phenolic resin (c) is free of methylol groups or substituted methylol groups. However, it may contain methylol or substituted methylol groups in a minute amount of up to 0.01 mole per mole of the total phenol component. The melting point of this starting novolak phenolic resin (c) is ordinarily 50 to 120°C. and preferably 60 to 90°C. As the bifunctional phenol, trifunctional phenol and aldehyde constituting the novolak phenolic resin (c), those mentioned before can be used. This starting novolak type phenolic resin (c) can easily be obtained by polycondensing the phenol and aldehyde in the presence of an acid catalyst by known procedures. In this starting novolak phenolic resin, it is indispensable that the content of the trifunctional phenol in the total phenol component should be no higher than 30 mole %. If the content exceeds 30 mole %, when a high-molecular-weight novolak resin is prepared by the chain-extending reaction, crosslinking occurs and the resin gels with the result that an intended high-molecular-weight resin having a chain structure cannot be obtained. In order to obtain a high-molecular-weight resin having a chain structure, especially a linear high-molecular-weight resin, it is preferred that the content of trifunctional phenol in the phenol component of the starting novolak phenolic resin be low. The dimethylolated phenol (d) used as the other starting substance is a dimethylolation product of the above-mentioned bifunctional phenol and/or the above-mentioned trifunctional phenol. More specifically, the dimethylolated phenol (d) is a dimethylolated phenol represented by the general formula [VIII]: wherein two of the three R³ groups are the remaining R³ group is a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen atom or a hydroxyl group, R² represents a hydrogen atom, a methyl group or a halogenated methyl group, and R represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a halogen atom or a hydroxyl group. A mixture of two or more of dimethylolated phenols of the general formula [VIII] may be used as the dimethylolated phenol (d). When one dimethylolated phenol is used, it is preferred that the dimethylolated phenol (d) be a dimethylolation product of a bifunctional phenol represented by the general formula [I]. When a mixture of two or more of dimethylolated phenols of the general formula [VIII] is used as the dimethylolated phenol (d), it is preferred that the content of a dimethylolation product of a bifunctional phenol of the general formula [I] in the mixture be at least 80 mole % and the content of a dimethylolation product of a trifunctional phenol of the general formula [III] in the mixture be up to 20 mole %. It is especially preferred to use a mixture comprising at least 90 mole % of a dimethylolation product of a bifunctional phenol of the general formula [I] and up to 10 mole % of a dimethylolation product of a trifunctional phenol of the general formula [III]. As the mixture of at least two dimethylolated phenols, there can be mentioned, for example, dimethylolation products of mixtures of ortho-, meta- and para-isomers of alkylphenols and halogenated phenols. The dimethylolated phenol represented by formula [VIII] can be selected from dihydroxymethyl phenols such as 2,6-dihydroxymethylphenol and 2,4-dihydroxymethylphenol; dihydroxymethylcresols such as 4,6-dihydroxymethyl-2-cresol, 2,6-dihydroxymethyl-3-cresol, 4,6-dihydroxymethyl-3-cresol, 2,6-dihydroxymethyl-4-cresol and mixtures of two or more of these dihydroxymethylcresols; dihydroxymethyl-n-propylphenols such as 4,6-dihydroxymethyl-3-n-propylphenol, 2,6-dihydroxymethyl-3-n-propylphenol, 4,6-dihydroxymethyl-3-n-propylphenol, 2,6-dihydroxymethyl-4-n-propylphenol and mixtures of two or more of these dihydroxymethyl-n-propylphenols; dihydroxymethylisopropylphenols such as 4,6-di-hydroxymethyl-2-isopropylphenol, 2,6-dihydroxymethyl-3-isopropylphenol, 4,6-dihydroxymethyl-3-isopropylphenol, 2,6-dihydroxymethyl-4-isopropylphenol and mixtures of two or more of these dihydroxymethylisopropylphenols, similar dihydroxymethylation products of n-butylphenol, sec-butylphenol, tert-butylphenol, n-amylphenol, sec-amylphenol, tert-amylphenol, hexylphenol, heptylphenol, octylphenol, fluorophenol, chlorophenol, bromophenol and iodophenol; bis(methylhydroxymethyl)phenols such as 2,6-bis(1-methyl-1-hydroxymethyl)phenol and 2,4-bis(1-methyl-1-hydroxymethyl)-phenol; bis(methylhydroxymethyl)cresols such as 4,6-bis(1-methyl-1-hydroxymethyl)-2-cresol, 2,6-bis(1-methyl-1-hydroxymethyl)-3-cresol, 4,6-bis(1-methyl-1-hydroxymethyl)-3-cresol, 2,6-bis(1-methyl-1-hydroxymethyl)-4-cresol and mixtures of two or more of these bis(methylhydroxymethyl)cresols; similar bis(methylhydroxymethyl) compounds of n-propylphenol, isopropylphenol, n-butylphenol, sec-butylphenol, tert-butylphenol, n-amylphenol, sec-amylphenol, tert-amylphenol, hexylphenol, heptylphenol, octylphenol, fluorophenol, chlorophenol, bromophenol and iodophenol; and bis(chloromethylhydroxymethyl) compounds, bis(dichloromethylhydroxymethyl) compounds, bis(trichloromethylhydroxymethyl) compounds, bis(bromomethylhydroxymethyl) compounds, bis(dibromomethylhydroxymethyl) compounds and bis(tribromomethylhydroxymethyl) compounds of similar phenols. Dimethylolated phenols (d) represented by the general formula [VIII] in which two of the three R³ groups in the general formula [VIII] stand for a methylol group represented by the formula the remaining R³ group selected from a methyl group, an ethyl group, an isopropyl group, a sec-butyl group, a tert-butyl group, an octyl group and a chlorine atom, one of the two R groups is a hydrogen atom, the remaining R group is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms and R² stands for a hydrogen atom or a methyl group are preferred. Dimethylolated phenols of the general formula [VIII], in which two of the three R³ groups stand for a methyl group represented by the formula the remaining R³ group is a methyl, ethyl, isopropyl, sec-butyl or tert-butyl group, each R group stands for a hydrogen atom and R² is a hydrogen atom or methyl group, are especially preferred. A dimethylolation product of o-cresol and/or p-cresol is particularly especially preferred as the dimethylolated phenol (d). Any acid catalyst customarily used for the production of novolak phenolic resins can be used in the present invention. The acid catalyst can be selected from protonic acids such as nitric acid, sulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, toluenesulfonic acid and methane-sulfonic acid, boron trifluoride, boron trifluoride complexes such as boron-trifluoride-ether complex, and Lewis acids such as aluminum trichloride, tin tetrachloride, zinc chloride, ferric chloride and titanium tetrachloride. Preferably protonic acids, boron trifluoride, boron trifluoride complexes and aluminum trichloride are used. The use of nitric acid, sulfuric acid, boron trifluoride or a boron trifluoride complex is especially preferred. The acid catalyst is generally used in an amount of 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, per 100 parts by weight of the starting novolak phenolic resin. When the starting novolak phenolic resin contains an acid catalyst added at the step of forming this phenolic resin, since this catalyst exerts a catalytic activity, a fresh acid catalyst need not be added for the polycondensation. In this polycondensation reaction, the ratio between the starting novolak phenolic resin (c) and the dimethylolated phenol (d) is changed according to the desired number average molecular weight of the resulting high-molecular weight novolak resin. As the molar ratio of the dimethylolated phenol (d) to the starting novolak substituted phenolic resin (c) is close to 1, a high-molecular-weight novolak resin having a higher number average molecular weight is obtained. The mixing ratio between the starting novolak phenolic resin (c) and the dimethylolated phenol (d) is such that the amount of the methylol groups in the dimethylolated phenol (d) is 0.5 to 1.5 equivalents, preferably 0.8 to 1.2 equivalents, especially preferably 0.9 to 1.1 equivalents, per equivalent of the hydroxyaryl units of the general formula [V] present at terminals of the molecule of the starting novolak type phenolic resin (c). The polycondensing reaction is readily advanced by heating and stirring the starting novolak phenolic resin (c) and the dimethylolated phenol (d) represented by the above general formula [VIII] in the presence of an acid catalyst while removing water formed by the reaction from the reaction system. The polycondensation reaction is carried out in the presence of a solvent. The solvent that is used can be toluene, o-dichlorobenzene, diphenyl ether or decalin. The solvent is used in an amount of 50 to 300 parts by weight, preferably 100 to 200 parts by weight, per 100 parts by weight of the starting novolak phenolic resin. The polycondensation temperature is ordinarily from 100 to 250°C. and preferably from 150 to 200°C. The time required for the polycondensation reaction is changed according to the reaction temperature and other conditions. The reaction time is not particularly critical. However, a reaction time of from 1 to 10 hours, preferably from 2 to 5 hours, is ordinarily used. After the polycondensation reaction, the reaction mixture is added to a liquid such as methanol, acetone or water which is not a solvent for the high-molecular-weight novolak resin to precipitate the high-molecular-weight novolak resin, or the solvent is removed from the reaction mixture by distillation under heating to recover the high-molecular-weight novolak resin. According to this embodiment, the reaction of both the starting substances is easily advanced and a high-molecular-weight novolak resin is formed most readily. Embodiment II A low-molecular-weight novolak phenolic resin (c) is reacted with a low-molecular-weight resol phenolic resin (e) as a chain extender in the presence of an acid catalyst. The resol phenolic resin (e) cannot be distinguished from the novolak recurring units when the resol phenolic resin (e) is included in the polymer chain of the resulting high-molecular-weight novolak resin. Accordingly, in the general formula [VII] representing the product resin, p is zero. The same low-molecular-weight novolak phenolic resins (d) as described before with reference to embodiment I can be used as the resin (d) in this embodiment. The resol phenolic resin (e) that is used as the other starting substance is a resol phenolic resin characterized by the following three features: (A) The phenol component constituting the resol phenolic resin (e) is a phenol component comprised mainly of at least one bifunctional phenol represented by the general formula [I], especially a phenol comprising 70 to 100 mole %, preferably 80 to 100 mole %, especially preferably 90 to 100 mole %, of at least one bifunctional phenol of the general formula [I] and up to 30 mole %, preferably up to 20 mole %, especially preferably up to 10 mole %, of a trifunctional phenol. The total amount of both the phenols is 100 mole %. (B) The aldehyde component comprises at least one aldehyde represented by the general formula [II]. (C) The number average molecular weight of the resol phenolic resin (e) is 250 to 1,200, preferably 350 to 1,000, especially preferably 400 to 800, as measured according to vapour pressure osmometry in N,N-dimethylacetamide as solvent. The structure of this starting resol phenolic resin (e) will now be described. The bifunctional phenol constituting this resol phenolic resin is present in the form of hydroxyarylene units represented by the general formula [IV] in the resin molecule and is present in the form of substituted hydroxymethylaryl units represented by the general formula [IX]: wherein R¹, R² and R are as defined above, at the terminals of the resin molecule. Furthermore, the trifunctional phenol is similarly present in the form of hydroxyarylene units as represented by the general formula [IV] in the resin molecule and is present in the form of methylol group-containing hydroxyarylene units as represented by the general formula [IX] at terminals of the resin molecule [in case of a trifunctional phenol, R¹ in the general formulae [IV] and [IX] stands for a hydrogen atom]. The aldehyde of general formula [II] constituting the starting resol phenolic resin is present in the form of methylene units represented by the general formula [VI] in the resin molecule and is present in the form of methylol group units represented by the general formula [X]: wherein R² is as defined above, at the terminals of the resin molecule. This starting resol phenolic resin (e) has a chain structure in which the hydroxyarylene units and methylene units are alternately arranged. More specifically, when the phenol component is comprised solely of a bifunctional phenol represented by general formula [I], the resol phenolic resin (e) has a linear chain structure. If the content of the trifunctional group is increased, the resol phenolic resin (e) has sometimes a branched chain structure. The ratio of the aldehyde component to the total phenol component in the resol phenolic resin (e) is such that the amount of the aldehyde is 0.90 to 1.0 mole, preferably 0.93 to 1.0 mole, per mole of the total phenol component. The melting point of this starting resol phenolic resin is ordinarily higher than 120°C. and preferably higher than 150°C. As the bifunctional phenol, trifunctional phenol and aldehyde constituting the starting resol phenolic resin, there can be used those described hereinbefore. This starting resol phenolic resin (e) can easily be obtained by polycondensing the phenol component with the aldehyde. The content of trifunctional phenol in the total phenol component resin must be no more than 30 mole %. If this content exceeds 30 mole %, cross-linking occurs in the resin at the polycondensation step and the resin is gelled. A high-molecular-weight having a chain structure cannot therefore be obtained. In order to obtain a high-molecular-weight novolak phenolic resin having a chain structure, especially a linear chain structure, it is preferred that the content of trifunctional phenol in the total phenol component of the starting resol phenolic resin be low. The ratio between the starting novolak phenolic resin (c) and resol phenolic resin (e) used for the polycondensation reaction depends on the intended number average molecular weight of the resulting high-molecular-weight novolak resin. As the molar ratio of the starting resol phenolic resin (e) to the starting novolak phenolic resin (c) is close to 1, a high-molecular-weight novolak phenolic resin having a higher number average molecular weight is obtained. The ratio between the starting novolak phenolic resin (c) and resol substituted phenolic resin (e) is such that the amount of methylol groups of the resol phenolic resin (e) is 0.5 to 1.5 equivalents, preferably 0.8 to 1.2 equivalents, especially preferably 0.9 to 1.1 equivalents, per equivalent of the hydroxyaryl units of general formula [V] present at the terminals of the molecule of the starting novolak phenolic resin (c). The polycondensation reaction can readily be advanced by heating and stirring the starting novolak phenolic resin (c) and resol phenolic resin (e) in the presence of an acid catalyst to effect the reaction while removing water formed by the reaction from the reaction system. Any acid catalyst mentioned before with reference to the embodiment I can be used also in this embodiment in the amount described before. The other reaction conditions may be the same as those described before with reference to the embodiment I. Although both the resol phenolic resin and the novolak phenolic resin are independently prepared in this embodiment, the process of this embodiment is advantageous in that a substantially linear high-molecular-weight novolak resin can be prepared in a high yield. Embodiment III A low-molecular-weight novolak phenolic resin (c) is reacted and polycondensed with a chain extender (f) selected from an aldehyde, a ketone, a diol and a dihalide in the presence of an acid catalyst. In this embodiment, divalent hydrocarbon groups derived from the chain extender are included in the polymer chain in such a manner that novolak recurring unit blocks are connected with one another through these divalent hydrocarbon groups as intervening groups. Accordingly, p in the general formula [VII] representing the resulting high-molecular-weight novolak resin is 1. As the starting low-molecular-weight novolak phenolic resin (c), there may be used those mentioned before with reference to embodiment I. As the chain extender (f), there are used aldehydes, ketones, diols or dihalides capable of introducing into the phenol ring a divalent hydrocarbon group Y in the general formula [VII], especially an alkylidene group, an alkylene group, a cycloalkylene group, a cycloalkylidene group, an arylalkylidene group, an arylalkylene group or an arylene-bis-alkylene group, by the reaction with the novolak type substituted phenolic resin (c). Appropriate aldehydes and ketones are represented by the general formula [XI]: wherein R⁴ stands for a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, R⁵ stands for a hydrogen atom, an alkyl group having 1 to 8 carbon atoms or an aryl group having 6 to 10 carbon atoms, and R⁴ and R⁵ may be bonded together through the intervening carbonyl carbon atom to form a cycloalkane. Appropriate diols and dihalides are represented by the general formula [XII]: X―Y―X [XII] wherein Y is as defined above and X stands for a hydroxyl group or a halogen atom. Specific examples of the chain extender (f) include aliphatic aldehydes of the general formula [II] exemplified before; aliphatic aldehydes such as formaldehyde (including formalin), acetaldehyde, propionaldehyde, butylaldehyde, isobutylaldehyde, valeraldehyde, isovaleraldehyde; aliphatic ketones such as acetone, methylethylketone, diethylketone, methylisopropylketone, methylisobutylketone, alkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol and hexylene glycol; alkylene dihalides such as ethylene fluoride, ethylene chloride, ethylene bromide, ethylene iodide, propylene fluoride, propylene chloride, propylene bromide, butylene chloride, butylene bromide, pentylene chloride, pentylene bromide, hexylene chloride and hexylene bromide; cycloalkyl aldehydes such as cyclohexylaldehyde; cycloalkylene glycols such as cyclopentyleneglycol, cyclohexylene glycol and methylcyclohexylene glycol; cycloalkylene dihalides such as cyclopentylene chloride, cyclohexylene chloride and methylcyclohexylene chloride; alicyclic ketones such as cyclopentanone and cyclohexanone; cycloalkylidene dihalides such as cyclohexylidene dichloride; aromatic aldehydes such as benzaldehyde and tolualdehyde; aromatic ketones such as acetophenone, methyltolyl ketone, ethylphenyl ketone, propylphenyl ketone and benzophenone; arylalkylidene diols such as benzylidene diol and xylidene diol; arylalkylidene dihalides such as benzyl fluoride, benzyl chloride, benzyl bromide, xylidine chloride and xylidine bromide; arylalkylene glycols such as styrene glycol, α-methylstyrene glycol and p-methyl-styrene glycol; arylalkylene dihalides such as styrene dibromide, styrene dichloride, styrene dibromide, α-methylstyrene dichloride, α-methylstyrene dibromide and p-methylstyrene dichloride; xylylene glycols such as o-xylylene glycol, m-xylylene glycol and p-xylylene glycol; arylene-bis-alkylene glycols such as o-bis(1-hydroxyethyl)benzene, m-bis(1-hydroxyethyl)benzene and p-bis(1-hydroxyethyl)-benzene; and arylene-bis-alkylene dihalides such as o-xylylene chloride, m-xylylene chloride, p-xylylene chloride, o-xylylene bromide, m-xylylene bromide, p-xylylene bromide, o-bis(1-chloroethyl)benzene, m-bis(1-chloroethyl)benzene and p-bis(1-chloroethyl)benzene. As the molar ratio of the chain extender (f) to the starting novolak phenolic resin (c) is close to 1, a high-molecular-weight novolak resin having a higher number average molecular weight is obtained. The ratio between the starting novolak phenolic resin (c) and chain extender (f) used for the polycondensation reaction is such that the amount of the reactive functional group of the chain extender (f) is 0.5 to 1.5 equivalents, preferably 0.8 to 1.2 equivalents, especially preferably 0.9 to 1.1 equivalents, per equivalent of the hydroxyaryl units of the general formula [V] which are present at the terminals of the molecule of the starting novolak phenolic resin (c). The polycondensation reaction is readily advanced by heating and stirring the starting novolak phenolic resin (c) and chain extender (f) in the presence of an acid catalyst while removing water formed by the reaction from the reaction system. As the acid catalyst, those mentioned before with reference to the embodiment I can be used in amounts described before with reference to the embodiment I. The other reaction conditions may be the same as those described before with reference to the embodiment I. According to this embodiment, units of the chain extender (f), which are different from the novolak recurring units, are included between the novolak recurring units. When an aldehyde or dihalide is used as the chain extender, the process of this embodiment is especially advantageous in that the polycondensation reaction can be accomplished very easily. Embodiment IV A phenol (g) comprised mainly of a bifunctional phenol is reacted with a low-molecular-weight resol phenolic resin (e) in the presence of an acid catalyst to effect polycondensation. In this embodiment, as in embodiment II, the resol phenolic resin (e) cannot be distinguished from the novolak recurring units when included in the molecule chain. Accordingly, in the general formula [VII] representing the resulting high-molecular-weight novolak resin, p is zero. The starting phenol (g) comprises 70 to 100 mole %, preferably 80 to 100 mole %, especially preferably 90 to 100 mole %, of at least one bifunctional phenol represented by general formula [I] and up to 30 mole %, preferably up to 20 mole %, especially preferably up to 10 mole %, of a trifunctional phenol represented by general formula [III]. The bifunctional and trifunctional phenols exemplified before may be used. The resol phenolic resin (e) described before with reference to the embodiment II can be used also in this embodiment. The ratio between the starting phenol (g) and resol phenolic resin (e) used for the polycondensation reaction depends on the intended number average molecular weight of the resulting high-molecular-weight novolak resin. As the molar ratio of the starting resol phenolic resin (e) to the starting phenol (g) is close to 1, a high-molecular-weight novolak resin having a higher number average molecular weight is obtained. The ratio between the starting phenol (g) and resol phenolic resin (e) used for the polycondensation reaction is such that the amount of the methylol group of the resol phenolic resin (e) is 1 to 3 equivalents, preferably 1.6 to 2.4 equivalents, especially preferably 1.8 to 2.2 equivalents, per mole of the starting phenol (g). The polycondensation reaction can easily be advanced by heating and stirring the starting phenol (g) and resol phenolic resin (e) in the presence of an acid catalyst while removing water formed by the reaction from the reaction system. Acid catalysts described before with reference to the embodiment I may similarly be used in the same amounts as described before with reference to the embodiment I except that the amounts are determined based on the resol type phenolic resin. Other reaction conditions are the same as those described before with reference to the embodiment I. When the substantially linear high-molecular-weight novolak resin of the present invention is combined with setting resins such as epoxy resins, urethane resins, melamine resins, polybismaleimide resins, alkyd resins, unsaturated polyesters, conventional novolak phenolic resins and resol phenolic resins, resin compositions having highly improved heat resistance and mechanical properties can be obtained. Resin compositions comprising a setting resin and a high-molecular-weight novolak resin are described and claimed in EPC Application No. 80304743.0 filed on even date herewith and published as EP―A2―0032060 on 15th July 1981. Furthermore, the substantially linear high-molecular-weight novolak resin of the present invention can be used for a viscosity increaser for a rubber, a tackifier for an adhesive and for a printing ink, a paint and an ink for a pressure-sensitive copying paper. The following Examples illustrate the present invention. Referential Example 1 A reaction vessel was charged with 108 g p-cresol (1 mole), 77 g (0.95 mole as HCHO) of 37% formalin and 0.1 ml of 35% hydrochloric acid, and reaction was carried out for 1 hour at 90°C. and for another 1 hour at 120°C. under reflux. Then, dehydration and concentration were conducted under a reduced pressure of 100 mmHg and when the temperature of the reaction mixture was 150°C., the reaction mixture was taken out from the reaction vessel, cooled and solidified to obtain 108 g of a resin. The number average molecular weight M n of this resin was 510 as measured according to the vapor pressure osmometry in dimethylacetamide at 90°C., and the ratio of M w/ M n determined from the results of gel permeation chromatography was 1.4. The melting point of the resin was 83°C. as measured according to the microscopic method. The resin was dissolved in pyridine-d₅ and the ¹H nuclear magnetic resonance spectrum was determined to obtain results shown in Table 1. From the foregoing results, it was confirmed that the novolak p-cresol/formaldehyde resin obtained according to the above-mentioned method hardly contains a methylol group at the molecule terminal and was a linear structure in which p-cresol units and methylene units are alternately arranged. Furthermore, since this novolak p-cresol/formaldehyde resin was completely dissolved in dimethylacetamide, pyridine, tetrahydrofuran and the like, it was confirmed that no three-dimensional cross-linked structure (gelled portion) is formed. Referential Examples 2 to 4 Procedures of Referential Example 1 were repeated in the same manner except that o-cresol, p-tert-butylphenol were used in amounts indicated in Table 2 instead of p-cresol. The number average molecular weight ( M n) and structure of each of the so obtained resins were determined according to the methods described in Referential Example 1. It was confirmed that each of these resins is a novolak phenol/formaldehyde resin having a linear structure in which the phenol units and methylene units are alternately arranged, as in the product of Referential Example 1. Furthermore, since these resins were completely dissolved in dimethylacetamide, pyridine, tetrahydrofuran and the like, it was confirmed that a three-dimensional crosslinked structure (gelled portion) is not formed. Referential Examples 5 to 7 p-Cresol was mixed with m-cresol as shown in Table 4, and the mixture, 77 g (0.95 mole as HCHO) of 37% formalin and 0.1 ml of 35% hydrochloric acid were charged in a reaction vessel. Reaction was carried out for 1 hour at 90°C, and for another 1 hour at 120°C. under reflux. Dehydration and concentration were then conducted under a reduced pressure of 100 mmHg, and when the temperature of the reaction product was 150°C., the reaction product was taken out from the reaction vessel, cooled and solidified to obtain 108 g of a resin. The number average molecular weight ( M n), molecular weight distribution and melting point of the obtained resin were determined according to the vapor pressure osmometry (at 90°C. in dimethylacetamide), gel permeation chromatography and microscopic method, respectively. The ratio between the p-cresol and m-cresol units constituting the resin was determined from data of ¹H nuclear magnetic resonance spectrum determined in pyridine-d₅. The obtained results are shown in Table 3. The structures of the obtained resins were examined in the same manner as described in Referential Example 1. It was found that the resins obtained in Referential Examples 5 and 6 contain both the p-phenol and m-phenol units as the phenol units and they are novolak phenol/formaldehyde resins having a linear structure in which these phenol units and methylene units are alternately arranged and parts of the m-phenol units are branched. Since these resins were completely dissolved in dimethylacetamide, it was confirmed that these resins do not contain a three-dimensional crosslinked structure (gelled portion). The resin obtained in Referential Example 7 was found to have a structure in which the p-phenol and m-phenol units are contained as the phenol units, and these phenol units and the methylene units are alternately arranged. However, since the resin contained a portion insoluble in dimethylacetamide, it was confirmed that a gelled portion, that is, a three-dimensional crosslinked structure, is partially contained in the resin. Properties of these novolak phenol/formaldehyde resins are shown in Table 3. Example 1 A reaction vessel was charged with 100 g of a novolak p-cresol/formaldehyde resin ( M n=510) obtained according to the conventional process shown in Referential Example 1, 31.1 g of 2,6-dimethylol-p-cresol, 0.28 ml of 60% nitric acid and 100 ml of o-dichlorobenzene, and reaction was carried out at 175°C. for 4 hours under stirring. The reaction mixture was thrown into 1 l of methanol, and after removal of the unreacted substances, the reaction product was dried to obtain 120 g (the yield being 97%) of a resin. The number average molecular weight M n was 5550 as measured according to the vapor pressure osmometry (in dimethylacetamide at 90°C.). The molecular weight distribution ( M w/ M n) of the resin as determined according to gel permeation chromatography was 6.2 and the melting point of the resin as measured by the microscopic method was higher than 300°C. Data of ¹H nuclear magnetic resonance spectrum of the resin as determined in pyridine-d₅ are shown in Table 5. From the data, the presence of the methylene proton of the methylol group in the vicinity of the ζ value of 5.3 was not observed. Accordingly, it was confirmed that the obtained resin is a novolak p-cresol/formaldehyde resin having a linear structure in which the p-cresol units and the methylene units are alternately arranged. Since the resin was completely dissolved in dimethylacetamide, it was confirmed that a three-dimensional crosslinked structure (gelled portion) is not present. Comparative Example 1 A reaction vessel was charged with 108 g (1 mole) of p-cresol, 168 g (1 mole) of 2,6-dimethylol-p-cresol, 540 ml of o-dichlorobenzene and 0.4 ml of 60% nitric acid, and reaction was carried out at 175°C. for 4 hours under stirring. The obtained resin was thrown into 5 l of methanol to remove the unreacted substances and the product was dried to obtain 87 g (the yield being 41 %) of a resin. The number average molecular weight M n of the resin as measured according to the vapor pressure osmometry was 1080, and the molecular weight distribution M w/ M n as determined by gel permeation chromatography was 1.4. The melting point of the resin as determined according to the microscopic method was 230°C. When the structure of the resin was examined in the same manner as described in Example 1, it was found that the resin is a novolak p-cresol/formaldehyde resin having a linear structure in which the p-cresol units and the methylene units are alternately arranged and a three-dimensional crosslinked structure (gelled portion) is not present. Examples 2 to 4 Procedures of Example 1 were repeated in the same manner except that a novolak o-cresol/formaldehyde, p-tert-butylphenol/formaldehyde or p-chlorophenol/formaldehyde resin shown in Table 6 was used instead of the novolak p-cresol/formaldehyde resin used in Example 1. The number average molecular weight M n and structure of each of the obtained resins were determined according to the same methods as described in Example 1. It was found that each of the obtained resins is a novolak phenol/formaldehyde resin having a linear structure in which the phenol units and the methylene units are alternately arranged, as in the product of Example 1. Since each of these resins was completely dissolved in dimethylacetamide, it was confirmed that a three-dimensional crosslinked structure (gelled portion) is not present in any of the obtained resins. Properties of these resins are shown in Table 6. Examples 5 and 6 Procedures of Example 1 were repeated in the same manner except that 100 g of the novolak m-cresol/p-cresol/formaldehyde copolycondensed resins prepared according to the methods described in Referential Examples 5 and 6 were used. The structures of the obtained resins were determined according to the method described in Referential Example 5. It was found that each of the obtained resins is a novolak phenol/formaldehyde resin having a linear structure in which both the p-phenol and m-phenol units are contained as the phenol units, and these phenol units and the methylene units are alternately arranged and branches are present in parts of the m-phenol units. Since each of these resins was completely dissolved in dimethylacetamide, it was confirmed that a gelled portion, that is, a three-dimensional cross-linked structure, is not present in any of these resins. The obtained results are shown in Table 7. Examples 7 to 9 The novolak p-cresol/formaldehyde resin ( M n=510, M w/ M n= 1.4, melting point=83°C.) obtained according to the method described in Referential Example 1 and 2,6-dimethylol-p-cresol were mixed as shown in Table 8, and the mixture was charged in an autoclave together with 0.03 ml of 60% nitric acid and 100 ml of toluene and reaction was carried out at 175°C. for 4 hours under stirring. The reaction mixture was thrown in 500 ml of methanol to precipitate the resin, and the recovered product was dried to obtain a high-molecular-weight resin. The number average molecular weights M n, molecular weight distributions M w/ M n and structures of the obtained resins were determined in the same manner as described in Example 1. Since each of these resins was completely dissolved in dimethylacetamide, it was confirmed that a three-dimensional crosslinked structure (gelled portion) is not present in any of the obtained resins. Basic properties of the obtained resins are shown in Table 8. Example 10 A reaction vessel was charged with 108 g (1 mole) of p-cresol, 162 g (2 moles as HCHO) of 37% formalin and 4 g (0.1 mole) of sodium hydroxide, and reaction was carried out at 80°C. for 4 hours. The reaction mixture was cooled to room temperature, neutralized with 2N hydrochloric acid and washed with water to obtain 98 g of a resol p-cresol/formaldehyde resin. The number average molecular weight M n of the obtained resin was 330 as determined according to the vapor pressure osmometry in dimethylacetamide at 90°C. A reaction vessel was charged with 18 g of the so obtained resol p-cresol/formaldehyde resin, 40 g of the the novolak p-cresol/formaldehyde resin obtained in Comparative Example 1, 40 ml of o-dichlorobenzene and 0.03 ml of 60% nitric acid, and reaction was carried out at 175°C. for 4 hours. The reaction mixture was thrown into 500 ml of methanol to precipitate the resin and the recovered product was dried to obtain 54 g of a resin. The number average molecular weight M n of the obtained resin was 2800 as determined according to the vapor pressure osmometry in dimethylacetamide at 90°C., and the molecular weight distribution M w/ M n of the resin as determined according to gel permeation chromatography was 3.4. The melting point of the resin as determined according to the microscopic method was higher than 300°C. Since the resin was completely dissolved in dimethylacetamide, it was confirmed that a three-dimensional crosslinked structure (gelled portion) is not present. Examples 11 to 13. Procedures of Example 10 were repeated in the same manner except that the reaction temperature was changed as indicated in Table 9. The number average molecular weight M n, the molecular weight distribution M w/ M n and melting point of each of the obtained resins were determined in the same manner as described in Example 10 to obtain results shown in Table 9. Example 14 A reaction vessel was charged with 31 g of the resol p-cresol/formaldehyde resin obtained according to the method described in Example 10, 10.8 g (0.1 mole) of p-cresol, 40 ml of o-dichlorobenzene and 0.15 ml of 60% nitric acid, and reaction was carried out at 175°C. for 4 hours. The reaction mixture was thrown into 500 ml of methanol to precipitate a resin, and the recovered product was dried to obtain 36 g of a resin. The number average molecular weight M n of the obtained resin was 2800 as determined according to the vapor pressure osmometry in dimethylacetamide at 90°C., and the molecular weight distribution M w/ M n of the resin as determined according gel permeation chromatography was 3.2. The melting point of the resin was higher than 300°C. as determined according to the microscopic method. The structure of the obtained resin was examined in the same manner as described in Example 1. It was found that the obtained resin has a linear structure in which the p-cresol units and the methylene units are alternately arranged. Since the resin was completely dissolved in dimethylacetamide and the like, it was confirmed that a three-dimensional crosslinked structure (gelled portion) is not present. Comparative Example 2 A reaction vessel equipped with a thermometer, a stirrer and a reflux cooler was charged with 94 g (1 mole) of phenol, 70 g (0.86 mole) of 37% formalin and 1 ml (0.274 millimole) of 1 % by weight hydrochloric acid, and the mixture was heated and stirred and reaction was conducted for 4 hours from the point of initiation of refluxing. Then, 1 g (5.3 millimoles) of p-toluenesulfonic acid was added to the reaction mixture and a device for dehydration under reduced pressure was attached to the reaction vessel. Removal of water and phenol was conducted under heating under a reduced pressure of 10 mmHg until the temperature of the reaction product was 180°C. As the result, 88 g (the yield being 84%) of a brown solid resin was obtained. It was found that 36% by weight of the obtained resin is insoluble in N,N-dimethylacetamide and the resin contains a gelled portion (three-dimensional crosslinked structure). It also was found that the remaining 74% by weight of the resin is soluble in N,N-dimethylacetamide and consists of a novolak phenol/formaldehyde resin having a branched chain structure. The average molecular weight M n of this branched novolak phenol/formaldehyde resin was 1090 as determined according to the vapor pressure osmometry. Comparative Example 3 A reaction vessel equipped with a thermometer, a stirrer and a reflux cooler was charged with 94 g (1 mole) of phenol, 70 g (0.86 mole) of 37% formalin and 1 ml (0.274 millimole) of 1 % by weight hydrochloric acid, and the mixture was heated and stirred and reaction was conducted for 4 hours from initiation of refluxing. Then, 1 g (5.3 millimoles) of p-toluene-sulfonic acid was added to the reaction mixture and a device for dehydration under reduced pressure was attached to the reaction vessel. Removal of water and phenol was conducted under heating under a reduced pressure of 10 mmHg until the temperature of the reaction product was 180°C. and removal of water and phenol was then conducted for another 30 minutes. As the result, 70 g (the yield being 67%) of a brown solid resin was obtained. It was found that 58% by weight of the obtained resin is insoluble in N,N-dimethylacetamide and the resin contains a gelled portion (three-dimensional crosslinked structure). It also was found that the remaining 42% by weight of the resin is soluble in N,N-dimethylacetamide and consists of a novolak phenol/formaldehyde resin having a branched chain structure. The average molecular weight M n of this branched novolak phenol/formaldehyde resin was 470 as determined according to the vapor pressure osmometry. Comparative Example 4 A reaction vessel equipped with a thermometer, a stirrer and a reflux cooler was charged with 108 g (1 mole) of p-cresol, 70 g (0.86 mole) of 37% formalin and 1 ml (0.274 millimole) of 1 % by weight hydrochloric acid, and the mixture was heated and stirred and reaction was conducted for 4 hours from initiation of refluxing. Then, 1 g (5.3 millimoles) of p-toluene-sulfonic acid was added to the reaction mixture and a device for dehydration under reduced pressure was attached to the reaction vessel. Removal of water and p-cresol was conducted under heating under a reduced pressure of 10 mmHg until the temperature of the reaction product was 180°C. As the result, 89 g (the yield being 75%) of a brown solid resin was obtained. Since the obtained resin was completely dissolved in N,N-dimethylacetamide, it was confirmed that the resin is free of a three-dimensional crosslinked structure (gelled portion). It was confirmed that the obtained resin is a novolak p-cresol/formaldehyde resin having a linear molecular structure. The number average molecular weight M n of the obtained resin was 670 as determined according to the vapor pressure osmometry. Example 15 An autoclave having a capacity of 500 ml was charged with 100 g of the novolak p-cresol/formaldehyde resin ( M n=510) prepared according to the method illustrated in Referential Example 1, 27.6 g of p-xylylene glycol, 0.28 ml of 60% nitric acid and 270 ml of toluene, and reaction was carried out at 175°C. under stirring for 4 hours. The reaction mixture was dissolved in 1 l of methanol to remove unreacted substances, and the reaction product was dried to obtain 72 g (the yield being 60% ). The number average molecular weight M n of the obtained resin was 2000 as determined according to the vapor pressure osmometry in dimethylacetamide at 90°C., and the molecular weight distribution M w/ M n of the resin was 2.5 as determined according to gel permeation chromatography. The melting point of the resin was higher than 300°C. as determined according to the microscopic method. The structure of the resin was examined in the same manner as described in Referential Example 1. It was found that the resin has a novolak p-cresol/formaldehyde resin skeleton. Since a high-molecular-weight resin different from the starting resin was formed, it was confirmed that the starting low-molecular-weight novolak p-cresol/formaldehyde resin was reacted with p-xylylene glycol and the molecular weight was increased by alternate arrangement and connection of the starting novolak p-cresol/formaldehyde units and p-xylylene units, and that novolak p-cresol/formaldehyde resin units were connected to the molecule terminals of the formed resin. Since the formed resin was completely dissolved in dimethylacetamide, tetrahydrofuran and the like, it was confirmed that the formed resin is free of a three-dimensional crosslinked structure (gelled portion) and is substantially linear. Examples 16 to 23 Procedures of Example 15 were repeated in the same manner except that a chain extender shown in Table 10 was used instead of p-xylylene glycol used in Example 15. The number average molecular weights M n and structures of the obtained resins were determined according to the methods described in Example 15. In each of the obtained resins, it was confirmed that the molecule terminals of the starting novolak p-cresol/formaldehyde resins were reacted with the chain extender shown in Table 10 and the molecular weight was increased by alternate arrangement and connection of the novolak p-cresol/formaldehyde resin units and the units of the chain extender shown in Table 10. It also was confirmed that the novolak p-cresol/formaldehyde resin units were connected to the molecule terminals of the formed resin. Since the formed resin was completely dissolved in dimethylacetamide, tetrahydrofuran and the like, it was confirmed that each of the formed resins is free of a three-dimensional crosslinked structure (gelled portion) and is substantially linear. Properties of the obtained resins are shown in Table 10. Examples 24 to 26 Procedures of Example 15 were repeated in the same manner except that the novolak o-cresol/formaldehyde resin obtained in Referential Example 2 (Example 24), the novolak p-tert-butylphenol/formaldehyde resin obtained in Referential Example 3 (Example 25) and the novolak p-chlorophenol/formaldehyde resin obtained in Referential Example 4 (Example 26) were used as shown in Table 11 instead of the novolak p-cresol/formaldehyde resin used in Example 15. The number average molecular weights M n and molecular weight distributions M w/ M n of the obtained resins were determined in the same manner as described in Example 15. The structure of the formed resins were examined in the same manner as described in Example 15 and it was confirmed that in each of the obtained resins, the molecule terminals of the starting novolak phenol/formaldehyde resin were reacted with p-xylylene glycol and the molecular weight was increased by alternate arrangement and connection of the novolak substituted phenol/formaldehyde resin units and the p-xylylene units, and that the novolak phenol/formaldehyde resin units were connected to the molecule terminals of the formed resin. Since the obtained resins were completely dissolved in dimethylacetamide, tetrahydrofuran and the like, it was confirmed that each of the formed resins is free of a three-dimensional crosslinked structure (gelled portion) and is substantially linear. Properties of the so obtained resins are shown in Table 11. Examples 27 and 28 Procedures of Example 15 were repeated in the same manner except that 100 g of the novolak m-cresol/p-cresol/formaldehyde copolycondensed resin obtained Referential Example 5 or 6 was used. The structures of the obtained resins were examined in the same manner as described in Example 15. It was confirmed that in each of the obtained resins, a novolak m-cresol/p-cresol/formaldehyde copolycondensed resin skeleton was present. Since a high-molecular-weight resin different from the starting resin was formed, it was confirmed that the starting low-molecular-weight novolak m-cresol/p-cresol/formaldehyde copolycondences resin was reacted with p-xylylene glycol, and that the molecular weight was increased by alternate arrangement and connection of the novolak m-cresol/p-cresol/formaldehyde copolycondensed resin units and p-xylylene units. It also was found that the novolak m-cresol/p-cresol/formaldehyde resin units were connected to the molecule terminals of the formed resin. Since these resins were completely dissolved in dimethylacetamide, tetrahydrofuran and the like, it was confirmed that each of these resins is free of a three-dimensional crosslinked structure (gelled portion) and is substantially linear. Properties of the obtained resins are shown in Table 12. Example 29 An autoclave having a capacity of 500 ml was charged with 100 g of the novolak p-cresol/formaldehyde resin ( M n=510) obtained according to the customary method illustrated in Referential Example 1, 16.2 g of 37% formalin, 0.28 ml of 60% nitric acid and 270 ml of toluene, and reaction was carried out at 175°C. for 4 hours under stirring. The reaction mixture was thrown into 1 l of methanol to remove the unreacted substances, and the recovered product was dried to obtain 92 g (the yield being 74%) of a resin. The number average molecular weight M n of the resin was 2020 as determined according to the vapor pressure osmometry, and the molecular weight distribution M w/ M n as determined according to gel permeation chromatography was 21. The melting point of the resin was higher than 300°C. as determined according to the microscopic method. Data of ¹H nuclear magnetic resonance spectrum of the obtained resin as determined in pyridine-d₅ are shown in Table 13. Since the presence of the methylene proton in the vicinity of the ζ value of 5.3 was not observed, it was confirmed that the obtained resin is a novolak p-cresol/formaldehyde resin having a linear structure in which no methylol group is present at the molecule terminals and the p-cresol units and methylene units are alternately arranged. Since the resin was completely dissolved in dimethylacetamide, it was confirmed that a three-dimensional crosslinked structure (gelled portion) is not included at all. Examples 30 to 32 Procedures of Example 29 were repeated in the same manner except that a compound shown in Table 14 was used as the chain extender. The number average molecular weights M n and structures of the obtained resins were determined in the same manner as described in Example 29. It was confirmed that each of the obtained resins is a novolak substituted phenol/formaldehyde resin having a linear structure in which the phenol units and methylene units are alternately arranged, as in the product obtained in Example 29. Since these resins were completely dissolved in dimethylacetamide, it was confirmed that a three-dimensional crosslinked structure (gelled portion) is not included in any of the obtained results. Properties of these resins are shown in Table 14. Examples 33 to 70 and Comparative Examples 5 to 16. The high-molecular-weight novolak substituted phenolic resins obtained in Examples 1 through 32 and novolak phenolic resins obtained in Referential Examples 1 through 7 were incorporated in setting type resins, and properties of the resulting setting resin compositions were examined and evaluated. The setting resin compositions used for evaluation of the properties were prepared according to any of the following methods [see Table 15]. Method (A) of preparation of setting resin compositions A mixture comprising 15 g of the novolak phenolic resin shown in Table 15, 25 g of a bisphenol A type epoxy resin (EPOMIK R-301 manufactured and supplied by Mitsui Petrochemical-Epoxy Co.), 150 g of fused silica, 0.25 g of a BF₃ · 2-methylimidazole complex and 0.75 g of a montanic acid wax was kneaded on a roll maintained at 80°C. for 7 minutes. After cooling, the kneaded mixture was pulverized to particles having a size of 7 to 100 mesh, and the pulverization product was press-molded in a mold maintained at 250°C. for 20 minutes under 100 Kg/cm² (actual pressure). The molded composition was post-cured at 250°C. for 30 minutes. The physical properties of the molded product were measured to obtain results shown in Table 15. Method (B) of preparation of setting resin compositions A mixture comprising 15 g of the novolak phenolic resin shown in Table 15, 25 g of a bisphenol A type epoxy resin (EPOMIK R-301 manufactured and supplied by Mitsui Petrochemical-Epoxy Co.), 95 g of fused silica, 0.25 g of a BF₃ · 2-methylimidazole complex and 0.75 g of a montanic acid wax was kneaded on a roll maintained at 80°C. for 7 minutes. After cooling, the kneaded mixture was pulverized to particles having a size of 7 to 100 mesh, and the pulverized composition was press-molded in a mold maintained at 250°C. for 20 minutes under 100 Kg/cm² (actual pressure). The molded composition was post-cured for 30 minutes, and the physical properties of the molded product were determined to obtain results shown in Table 15. Method (C) of preparation of setting resin compositions A mixture comprising 37 g of the high-molecular-weight p-cresol/formaldehyde resin shown in Table 15, 63 g of a bisphenol A type epoxy resin (EPOMIK R-140 manufactured and supplied by Mitsui Petrochemical-Epoxy Co.) and 0.1 g of 2-methylimidazole was dissolved in a mixed solvent comprising 25 g of methylethyl ketone and 5 g of methanol, and a glass cloth (Glass Cloth WE-18K-BZ2 manufactured and supplied by Nittobo Co.) was impregnated with the so formed varnish and press-molded at 170°C. for 1 hour. The press-molded product was post-cured at 180°C. for 8 hours to obtain a laminate sheet. The flexural strength of the laminate sheet was measured at 21, 150 and 180°C. to obtain results shown in Table 15. Method (D) of preparation of setting resin compositions A mixture comprising the novolak phenolic resin shown in Table 15, 25 g of a novolak phenol-epoxy resin (Epoxylated Phenol Novolak EPPN-201 manufactured and supplied by Nippon Chemical Co.), 95 g of fused silica, 0.25 g of a BF₃ · 2-methylimidazole complex and 0.75 g of a montanic acid wax was kneaded on a roll maintained at 80°C. for 7 minutes. After cooling, the kneaded mixture was pulverized to particles having a size of 7 to 100 mesh, and the pulverized composition was press-molded in a mold maintained at 250°C. for 20 minutes under 100 Kg/cm² (actual pressure). The press-molded composition was post-cured at 250°C. for 30 minutes, and the physical properties of the obtained molded product were measured to obtain results shown in Table 15. Method (E) of preparation of setting resin compositions A mixture comprising 15 g of the novolak phenolic resin shown in Table 15, 25 g of a bisphenol A type epoxy resin (EPOMIK R-301 manufactured and supplied by Mitsui Petrochemical-Epoxy Co.), 27 g of an inorganic filler shown in Table 15, 0.25 g of a BF₃ · 2-methylimidazole complex and 0.75 g of a montanic acid wax was kneaded on a roll maintained at 80°C. for 7 minutes. After cooling, the kneaded composition was pulverized to particles having a size of 7 to 100 mesh, and the pulverized composition was press-molded in a mold maintained at 80°C. for 20 minutes under 100 Kg/cm² (actual pressure). The press-molded product was post-cured at 250°C. for 30 minutes, and the physical properties of the molded product were determined to obtain results shown in Table 15. Method (F) of preparation of setting resin compositions A mixture comprising 100 g of the novolak phenolic resin shown in Table 15, 63 g of a bisphenol A type epoxy resin (EPOMIK R-140 manufactured and supplied by Mitsui Petrochemical-Epoxy Co.) and 1 g of a BF₃ · 2-methylimidazole complex was kneaded and press-molded in a mold maintained at 200°C. under 100 Kg/cm² (actual pressure) for 20 minutes. The press-molded composition was post-cured at 200°C. for 5 hours and reacted at 250°C. for 0.5 hour to form a cured molded product having physical properties shown in Table 15. Method (G) of preparation of setting resin compositions A mixture comprising 40 g of the novolak phenolic resin shown in Table 15, 60 g of novolak phenol-formaldehyde resin obtained in Comparative Example 2 (in Comparative Example 15, the novolak substituted phenolic resin was not used, but 100 g of the novolak phenol/aldehyde resin obtained in Comparative Example 2 was used), 10 g of hexamine as a curing agent, 67 g of wood flour as a filler and 1 g of stearic acid bisamide as an additive was sufficiently pulverized and blended and kneaded at 90 to 100°C. for 18 minutes to form a sheet. The sheet was pulverized and blended to form a molding material. The molding material was molded at 165°C. under 300 Kg/cm² for 5 minutes to obtain a molded product having physical properties shown in Table 15. Method (H) of preparation of setting resin compositions A molding material composition was prepared by blending 70 g of the novolak phenolic resin shown in Table 15, 30 g of solid resol phenol-formaldehyde resin prepared in Referential Example 8 illustrated hereinafter, 67 g of wood flour as a filler and 1 g of stearic acid bisamide as an additive. The composition was sufficiently pulverized and blended and roll-kneaded at 120°C. for 15 minutes. The obtained sheet was pulverized and blended, and the resulting molding material was molded at 180°C. under 300 Kg/cm² for 5 minutes to obtain a molded product having physical properties shown in Table 15. Referential Example 8 A reaction vessel was charged with 100 g (1.1 moles) of phenol, 90 g (1.1 moles as HCHO) of 37% formalin and 0.5 g of 25% aqueous ammonia, and reaction was carried out under reflux at 90 to 100°C. for 1.5 hours. The temperature was lowered at room temperature, and the separated water layer was removed. The obtained precondensate emulsion was heated again at 90 to 110°C. and water was removed under reduced pressure. When the temperature of the reaction product was 110°C., the reaction product was taken out from the reaction vessel and cooled and solidified to obtain 100 g of a resin. From the results obtained according to the vapor pressure osmometry and gel permeation chromatography, it was found that the obtained resin had a number average molecular weight M n of 440, a weight average molecular weight M w of 740 and a molecular weight distribution M w/ M n of 1.69. The melting point of the resin was 105°C. as determined according to the microscopic method.

Claims: 1. A process for the preparation of a high-molecular weight novolak phenolic resin by reacting (A)(i) a phenol component mainly comprising at least one bifunctional phenol represented by the general formula [I]: wherein two of the three R¹′s are hydrogen atoms and the remaining R¹ is an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen atom or a hydroxyl group, and the two R′s, which may be same or different, represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a halogen atom or a hydroxyl group, wherein the R¹ group which is not a hydrogen atom is in the para position with respect to the hydroxy group, or (ii) a novolak phenolic resin derived from a phenol component mainly comprising said bifunctional phenol of general formula [I] and an aldehyde represented by the general formula: R² - CHO [II] wherein R² represents a hydrogen atom, a methyl group or a halogenated methyl group, and having a number average molecular weight of from 250 to 1200, with (B) a chain extender selected from (i) dimethylolated bifunctional and trifunctional phenols, (ii) resol phenolic resins derived from a phenol component mainly comprising said bifunctional phenol of general formula [I] and said aldehyde of general formula [II] and having a number average molecular weight of from 250 to 1200, (iii) aldehydes, (iv)ketones, (v) diols and (vi) dihalides, with the proviso that when reactant (A) is the phenol component (i), the chain extender (B) is the resol phenolic resin (ii), so that at least 70 mole % of the phenol component in the final novolak phenolic resin is derived from said bifunctional phenol of general formula [I]; characterised in that said reaction is carried out in a solvent in the presence of an acid catalyst until the number average molecular weight of the final novolak phenolic resin is from 1,700 to 15,000 as measured by vapour pressure osmometry in N,N-dimethylacetamide as solvent, the ratio M w/ M n of the weight average molecular weight M w to the number average molecular weight M n is from 1.8 to 2.0 and the melting point of said resin is higher than 160°C. 2. A process according to claim 1, characterised in that the acid catalyst is a protonic catalyst, boron trifluoride, a boron trifluoride complex or aluminum trichloride. 3. A process according to claim 1 or 2, characterised in that the reaction is carried out at a temperature of 100 to 250°C. 4. A process according to any one of the preceding claims, characterised in that the acid catalyst is present in an amount of 0.01 to 10 parts by weight, per 100 parts by weight of the starting novolak phenolic resin (A)(ii) or the starting resol phenolic resin (B)(ii). 5. A process according to any one of the preceding claims wherein the number average molecular weight of the final novolak phenolic resin is 2000 to 10000. 6. A process according to any one of the preceding claims, characterised in that the phenol component (A)(i), the phenol component from which the novolak phenolic resin (A)(ii), or the phenol component from which the resol phenolic resin (B)(ii) is derived comprises 80 to 100 mole % of said bifunctional phenol of general formula [I] and up to 20 mole % of a trifunctional phenol, the total amount of both types of phenol being 100 mole %. 7. A process according to claim 6 characterised in that the phenol component (A)(i), the phenol component from which the novolak phenolic resin (A)(ii) or the phenol component from which the resol phenolic resin (B)(ii) is derived comprises 90 to 100 mole % of said bifunctional phenol of general formula [I] and up to 10 mole % of the trifunctional phenol. 8. A process according to any one of the preceding claims, characterised in that in said bifunctional phenol of general formula [I] the R¹ group which is not a hydrogen atom is a methyl, ethyl, isopropyl, sec-butyl, tert-butyl or octyl group or chlorine atom. 9. A process according to any one of the preceding claims, characterised in that the phenol component (A)(i), the phenol component from which the novolak phenolic resin (A)(ii) or the phenol component from which the resol phenolic resin (B)(ii) is derived comprises at least one trifunctional phenol represented by the general formula [III]: wherein each R which may be the same or different, stands for a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a halogen atom or a hydroxyl group. 10. A process according to claim 9, characterised in that in the trifunctional phenol of general formula [III] one of two R groups is a hydrogen atom and the remaining R group is a hydrogen atom or a methyl group, an ethyl group, an isopropyl group, a sec-butyl group, a tert-butyl group, an octyl group or a chlorine atom. 11. A process according to any one of the preceding claims, characterised in that the aldehyde of general formula [II] is formaldehyde or acetaldehyde. 12. A process according to any one of the preceding claims, characterised in that the novolak phenolic resin (A)(ii) or resol phenolic resin (B)(ii) has a number average molecular weight of 350 to 1000. 13. A process according to claim 12, characterised in that the number average molecular weight is 400 to 800. 14. A process according to any one of the preceding claims, characterised in that reactant (A) is the novolak phenolic resin (ii) and the chain extender (B) is the dimethylolated phenol (i), the ratio of the two reactants being such that the amount of methylol groups of the dimethylolated phenol (B)(i) is 0.5 to 1.5 equivalents per equivalent of the hydroxyaryl units at the molecule terminals of the novolak phenolic resin (A)(ii). 15. A process according to claim 14, characterised in that the ratio of the dimethylolated phenol (B)(i) to the novolak phenolic resin (A)(ii) is such that the amount of methylol groups of the dimethylolated phenol is 0.8 to 1.2 equivalents per equivalent of the hydroxyaryl units of the molecule terminals of the novolak phenolic resin. 16. A process according to any one of the preceding claims, characterised in that the chain extender (B)(i) comprises a dimethylolated phenol represented by the general formula [VIII]: wherein two of the three R³ groups are the remaining R³ group is a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen atom or a hydroxyl group, R² stands for a hydrogen atom, a methyl group or a halogenated methyl group, and R stands for a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a halogen atom or a hydroxyl group. 17. A process according to claim 16, characterised in that in the dimethylolated phenol of general formula [VIII], said remaining R³ group is a methyl, ethyl, isopropyl, sec-butyl or tert-butyl group and R² stands for a hydrogen atom. 18. A process according to any one of the preceding claims, characterised in that the chain extender (B)(i) comprises at least 80 mole % of a dimethylolated product of a bifunctional phenol represented by the general formula [I] and up to 20 mole % of a dimethylolated product of a trifunctional phenol represented by the general formula [III] as defined in claim 9. 19. A process according to claim 18, characterised in that the dimethylolated phenol of chain extender (B)(i) consists solely of a dimethylolated product of a bifunctional phenol represented by the general formula [I]. 20. A process according to any one of the preceding claims, characterised in that the dimethylolated phenol of chain extender (B)(i) is a dimethylolated cresol. 21. A process according to any one of claims 1 to 13, characterised in that the reactant (A) is the novolak phenolic resin (ii) and the chain extender (B) is the resol phenolic resin (ii) the ratio of the two reactants being such that the amount of methylol groups of the resol phenolic resin (B)(ii) is 0.5 to 1.5 equivalents per equivalent of the hydroxyaryl units at the molecule terminals of the novolak phenolic resin (A)(ii). 22. A process according to claim 21, characterised in that the ratio of the resol phenolic resin (B)(ii) to the novolak phenolic resin (A)(ii) is such that the amount of methylol groups of the resol phenolic resin is 0.8 to 1.2 equivalents per equivalent of the hydroxyaryl units at the molecule terminal of the novolak phenolic resin. 23. A process according to any one of claims 1 to 13, characterised in that the reactant (A) is the novolak phenolic resin (ii) and the chain extender (B) is (iii) an aldehyde, (iv) a ketone, (v) a diol or (vi) a dihalide, the ratio of the chain extender to the novolak phenolic resin being such that the amount of the functional groups of the chain extender is 0.5 to 1.5 equivalents per equivalent of the hydroxyaryl units at the molecule terminals of the novolak phenolic resin. 24. A process according to claim 23, characterised in that the ratio of the chain extender to the novolak phenolic resin is such that the amount of the functional groups of the chain extender is 0.8 to 1.2 equivalents per equivalent of the hydroxyaryl units at the molecule terminals of the novolak phenolic resin. 25. A process according to any one of claims 1 to 13, 23 or 24, characterised in that the molecular weight of the chain extender (B)(iii), (B)(iv), (B)(v) or (a)(vi) is 14 to 200. 26. A process according to any one of claims 1 to 13 or 23 to 25, characterised in that the chain extender (B)(iii) is an aliphatic aldehyde having up to 5 carbon atoms. 27. A process according to any one of claims 1 to 13 or 23 to 25, characterised in that the chain extender (B)(iv) is an aliphatic ketone having up to 6 carbon atoms. 28. A process according to any one of claims 1 to 13 or 23 to 25, characterised in that the chain extender (B)(v) or (B)(vi) is a compound represented by the general formula [XII]. X - Y - X [XII] wherein X stands for a hydroxyl group or a halogen atom, and Y stands for an alkylene geoup having 2 to 5 carbon atoms, an arylalkylidene group having 7 to 9 carbon atoms, an arylalkylene group having 8 to 10 carbon atoms or an arylene-bis-alkylene group having 8 to 10 carbon atoms. 29. A process according to any one of claims 1 to 13, characterised in that the reactant (A) is the phenol component (i) and the chain extender (B) is the resol phenolic resin (ii), the ratio of both the reactants being such that the amount of methylol groups of the resol phenolic resin is 1 to 3.0 equivalents per mole of said phenol component. 30. A process according to claim 29, characterised in that the ratio of the resol phenolic resin (B)(ii) to the phenol component (A)(i) is such that the amount of methylol groups of the resol phenolic resin is 1.6 to 2.4 equivalents per mole of said phenol. 31. A substantially linear, high-molecular-weight novolak phenolic resin which comprises substantially linear novolak recurring units formed by condensation of a phenol component comprising at least 70 mole % of at least one bifunctional phenol represented by the general formula [I] as defined in claim 1, wherein the R¹ group which is not a hydrogen atom is in the para position with respect to the hydroxy group, with at least one aldehyde represented by the general formula as defined in claim 1, said resin having a number average molecular weight of from 1,700 to 15,000 as measured by vapour pressure osmometry in N,N-dimethylacetamide as solvent, a ratio M w/ M n of the weight average molecular weight M w to the number average molecular weight M n of from 1.8 to 20 and a melting point higher than 160°C. 32. A resin according to claim 31, characterised in that it contains intervening groups consisting of a divalent hydrocarbon group between blocks of said novolak recurring units having a number average molecular weight of 250 to 1200, such that said intervening groups and said blocks alternate, said intervening groups being present in an amount of 0.5 to 1 mole per mole of said blocks. 33. A resin according to claim 31 or 32, characterised in that the number average molecular weight is 2000 to 10000. 34. A resin according to any one of claims 31 to 33, wherein the molecular weight distribution M w/ M n is from 2.0 to 10. 35. A resin according to any one of claims 31 to 34, characterised in that it has a polymer chain represented substantially by the general formula [VII]: wherein Z stands for a block of said substantially linear novolak recurring units, Y stands for an intervening group consisting of a divalent hydrocarbon group, p is 0 or 1, and n is zero or a number of at least 1. 36. A resin according to claim 35, characterized in that in said general formula [VII], p is 1, and the intervening group Y is selected from alkylidene groups having 1 to 4 carbon atoms, alkylene groups having 2 to 5 carbon atoms, arylalkylidene groups having 7 to 9 carbon atoms, arylalkylene groups having 8 to 10 carbon atoms and arylene-bis-alkylene groups having 8 to 10 carbon atoms. 37. A resin according to any one of claims 31 to 36, characterised in that said phenol component contains up to 30 mole % of a trifunctional phenol. 38. A resin according to claim 37, characterised in that the phenol component comprises 80 to 100 mole % of said bifunctional phenol of general formula [I] and up to 20 mole % of the trifunctional phenol, with the proviso that the total amount of both the phenols is 100 mole %. 39. A resin according to claim 38, characterised in that the phenol component comprises 90 to 100 mole % of said bifunctional phenol of general formula [I] and up to 10 mole % of the trifunctional phenol. 40. A resin according to any one of claims 37 to 39, characterised in that the trifunctional phenol is at least one phenol represented by the general formula [III]: wherein each R, which may be the same or different, stands for a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a halogen atom or a hydroxyl group. 41. A resin according to claim 40, characterised in that in said general formula [III] one of the two R groups is a hydrogen atom and the remaining R group is a hydrogen atom, a methyl, ethyl, isopropyl, sec-butyl, tert-butyl or octyl group or a chlorine atom. 42. A resin according to any one of claims 31 to 41, characterised in that in said bifunctional phenol of general formula [I] the R¹ group which is not a hydrogen atom is a methyl, ethyl, isopropyl, sec-butyl, tert-butyl or octyl group. 43. A resin according to any one of claims 31 to 42, characterised in that said aldehyde is formaldehyde or acetaldehyde.

Inventors: IWATA, TADAO, TAKEDA, NOBUYUKI
Applicants: MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1980
Main classification: C08G8
IPC codes: C08L63, C08L101, C08G8, C08L61