Document:

<PAGE>

                                                          Confidential Treatment
                                                                    Exhibit 10.1

PORTIONS OF THIS EXHIBIT HAVE BEEN OMITTED AND FILED SEPARATELY WITH THE
SECRETARY OF THE COMMISSION PURSUANT TO THE REGISTRANT'S APPLICATION OBJECTING
TO DISCLOSURE AND REQUESTING CONFIDENTIAL TREATMENT UNDER RULE 24b-2. THE
OMITTED PORTIONS HAVE BEEN MARKED WITH BRACKETS.

                               SECOND AMENDMENT

This Second Amendment is effective as of January 1, 2001 between Chevron
Phillips Chemical Company LP, formerly Chevron Chemical Company LLC, ("CPC") and
Radnor Chemical Corporation ("RCC"); StyroChem U.S., Ltd. ("SUS"); StyroChem
Canada, Ltd. ("SCL"); and Wincup Holdings, Inc. ("Wincup"). RCC, SUS, SCL and
Wincup will be referred to collectively as "Purchaser").

WHEREAS, the parties have previously entered into a Styrene Monomer Contract of
Sale ("Contract"), effective December 5, 1996, and amended October 1, 1998, and
desire to further amend such Contract;

NOW THEREFORE, in consideration of mutual covenants and agreements hereinafter
set forth, the parties agree as follows:

Section 2 is deleted in its entirety and replaced with the following:

     The quantity of Product to be sold and delivered hereunder will be a
     minimum of 150,000,000 pounds and a maximum of 175,000,000 pounds per
     calendar year, the exact quantity within said range at Purchaser's option.
     Annual Product quantities in excess of 175,000,000 pounds will be by mutual
     agreement of the parties.  Purchaser will nominate the quantity of Product
     within said range for the calendar year in question by providing CPC
     written notice prior to [_______] of the preceding calendar year.

Section 4, second paragraph, last two sentences are deleted in their entirety
and replaced with the following:

     For purposes of this Contract, the "Freight Allowance" for shipments of
     Product from St. James, Louisiana to Marietta, Ohio will be [__] U.S. cents
     per pound.  This Freight Allowance will be readjusted on [_____________]
     and each anniversary thereafter in accordance with any change in the
     Consumer Price Index for all Consumers published by the U.S. Department of
     Labor for the 12 month period then completed.

Section 5, paragraph (b) is deleted in its entirety and replaced with the
following:

     (b) Payment will be due for invoiced Product and Purchaser will pay CPC in
     immediately available U.S. dollars in accordance with the following
     schedule:

          Calendar Year                       Payment Terms
          -------------                       -------------
          October, November, December 2000     See attached Schedule A
          2001                                 See attached Schedule A
          2002 & thereafter                    [__] days from date of invoice

     In the event that the actual price and/or volume differs from the
     estimated price and/or volume set forth under [Schedule A], the invoice and
     payment amounts will be prorated accordingly to reflect the actual price
     and/or volume in question.

     Purchaser will make payment by check, except in the case of SCL which
     will make payment by wire transfer.

                                       1
<PAGE>

Section 7 is deleted in its entirety and replaced with the following:

     Performance under this Contract will be extended through December 31, 2006
     and continue for successive annual terms thereafter unless terminated by
     either party giving the other at least 12 months prior written notice,
     which termination will be effective at the end of the initial term or any
     annual extension thereof.

Section 9, paragraph (a) is revised by deleting the definition of the "Styrene
Contract" factor and replacing with the following new definition for said
factor:

     "Styrene Contract" = Styrene - Adjustment, where

          "Styrene" is the North America Styrene Contract price (cpp) for the
          month of delivery as published in the month-end issue of CMAI's
          Monomers Market Report for said month, and will be the low end of the
          ----------------------
          values if a range is reported; and

          "Adjustment" is equal to [____] cpp; provided, however, that if at any
          time during 2001, CMAI elects to reduce the North America Styrene
          Contract price by an amount which CMAI deems greater than the reported
          market reduction, the value of the "Adjustment" will be reduced by an
          amount equal to said non-market reduction. Example: If CMAI elects in
          January of 2001 to implement a [____] cpp non-market reduction in the
          North America Styrene Contract price, the "Adjustment" will be reduced
          from [____] cpp to [____] cpp effective January 2001. Notwithstanding
          the foregoing, in no event will the "Adjustment" hereunder be reduced
          to a value less than [____] cpp.

Section 9 is revised by the addition of the following new paragraph at the end:

     Notwithstanding anything contained in this Contract to the contrary, the
     purchase price of Product quantities, if any, purchased during any calendar
     year in excess of 175,000,000 pounds will be by agreement of the parties.

Section 10 is revised by the addition of the following new paragraphs at the
end:

     Notwithstanding anything contained in this Contract to the contrary,
     Product quantities, if any, purchased during any calendar year in excess of
     175,000,000 pounds will not be eligible for a rebate under this Section 10.

     During calendar year 2001 only, if BUYER purchases a minimum of 160,000,000
     pounds of Product, BUYER will be eligible for an additional rebate in the
     amount of [____] cpp on all pounds of Product purchased during said
     calendar year up to a maximum of 175,000,000 pounds.

Section 11 is deleted in its entirety.

Section 21 is revised by deleting the facsimile number for CPC and replacing
with the following new facsimile number:  "(713) 289-4180".

Section 24 is deleted in its entirety.

                                       2
<PAGE>

As so amended, the Contract will remain in full force and effect.

The parties have caused this Second Amendment to be executed by their duly
authorized representatives as of the date of respective signature, but effective
as of January 1, 2001.

Radnor Chemical Corporation            Chevron Phillips Chemical Company LP

By: /s/ Michael T. Kennedy             By: /s/ Andrew G. Singer
   ---------------------------            -------------------------------

Title: Chairman                        Title: GM, Styrene
      ------------------------               ----------------------------

Date: January 19, 2001                 Date: January 30, 2001
     -------------------------              -----------------------------

StyroChem U.S., Ltd.                   StyroChem Canada, Ltd.

By: /s/ Michael T. Kennedy             By: /s/ Michael T. Kennedy
   ---------------------------            ---------------------------

Title: Chairman                        Title: Chairman
      ------------------------               ------------------------

Date: January 19, 2001                 Date: January 19, 2001
     -------------------------              -------------------------

Wincup Holdings, Inc.

By: /s/ Michael T. Kennedy
   ---------------------------

Title: Chairman
      ------------------------

Date: January 19, 2001
     -------------------------

                                       3

                                  Schedule A

                                [_____________]<PAGE>

                                AMENDMENT NO. 4

                                      TO

                     THIRD AMENDED AND RESTATED REVOLVING
                         CREDIT AND SECURITY AGREEMENT

     THIS AMENDMENT NO. 4 (the "Amendment") is entered into as of March 29,
2001, by and among WinCup Holdings, Inc., Radnor Chemical Corporation, StyroChem
U.S., Ltd., Radnor Holdings Corporation ("Radnor"), Radnor Delaware, Inc.,
StyroChem Delaware, Inc. and WinCup Texas, Ltd. (collectively, the "U.S.
Borrowers"), StyroChem Europe (the Netherlands) B.V., StyroChem Finland Oy,
ThermiSol Denmark A/S, ThermiSol Sweden AB and ThermiSol Finland Oy
(collectively, the "European Borrowers", and together with the U.S. Borrowers,
the "Borrowers"), Bank of America, N.A. ("Bank of America") and each of the
other financial institutions which are or become parties hereto (collectively,
the "Lenders") and Bank of America, as administrative and collateral agent for
the Lenders (in such capacity, the "Agent").

                                   BACKGROUND
                                   ----------

     The Borrowers, the Lenders and the Agent are parties to a Third Amended and
Restated Revolving Credit and Security Agreement dated as of December 29, 1999,
as amended by Amendment No. 1 to Third Amended and Restated Revolving Credit and
Security Agreement dated as of March 13, 2000, Amendment No. 2 to Third Amended
and Restated Revolving Credit and Security Agreement dated as of May 16, 2000,
and Amendment No. 3 to Third Amended and Restated Revolving Credit and Security
Agreement dated as of December 8, 2000 (as may be further amended, supplemented
or otherwise modified from time to time, the "Loan Agreement") pursuant to which
the Lenders provide the Borrowers with certain financial accommodations.

     The Borrowers have requested certain modifications to the Loan Agreement.
Such modifications require the consent of the Required Lenders (as defined in
the Loan Agreement).  The Required Lenders have consented to the requested
modifications on the terms and conditions hereafter set forth.

     NOW THEREFORE, in consideration of any loan or advance or grant of credit
heretofore or hereafter made to or for the account of the Borrowers by any
Lender and the Agent, and for other good and valuable consideration, the receipt
and sufficiency of which are hereby acknowledged, the parties hereto hereby
agree as follows.

     1.   Definitions.  All capitalized terms not otherwise defined herein shall
          -----------
have the meanings given to them in the Loan Agreement.
<PAGE>

     2.   Amendment to Loan Agreement.  Subject to satisfaction of the
          ---------------------------
conditions precedent set forth in Section 3 below, the Loan Agreement is hereby
amended as follows:

          (a)  A new definition of "Additional Advances" is hereby added to the
Loan Agreement in the appropriate alphabetical order:

          "Additional Advances" shall mean any Revolving Advance made by the
           -------------------
     Lenders to the Borrowers from March 29, 2001 through and including August
     16, 2001, if (x) such Revolving Advance is made pursuant to Section
     2.1(a)(iii) or 2.1A(a)(iii) or (y) such Revolving Advance is made pursuant
     to the increase to the U.S. Borrowing Base or the European Borrowing Base,
     as applicable, permitted pursuant to Sections 2.1(a)(i)(x),
     2.1(a)(ii)(x)(A), 2.1(a)(ii)(y)(A), 2.1A(a)(i)(x) or 2.1A(ii)(y)(A), such
     increase to be measured against the U.S. Borrowing Base or the European
     Borrowing Base, as applicable, as otherwise calculated pursuant to Section
     2.1 utilizing the advance levels for Revolving Advances made on or after
     August 17, 2001.

          (b)  The definition of  "Applicable Margin" in Section 1.2 of the Loan
Agreement, is hereby amended in its entirety to read as follows:

          "Applicable Margin" for any period shall be determined by the ratio of
           -----------------
     Funded Indebtedness to EBITDA calculated for the most recent fiscal quarter
     with respect to the four fiscal quarters then ended which shall be subject
     to adjustment from time to time as set forth in Section 3.1 and Section
     3.3(b).  The Applicable Margin with respect to Eurodollar Rate Loans,
     Domestic Rate Loans and the Facility Fee provided for in Section 3.3(b)
     hereof, as the case may be, shall be the percentage set forth below as
     corresponds to the applicable ratio set forth below:

<TABLE>
<CAPTION>
            Funded Indebtedness                   Domestic         Eurodollar       Facility
                 To EBITDA                      Rate Margin       Rate Margin          Fee
                 ---------                      -----------       -----------          ---
<S>                                           <C>               <C>               <C>
Greater than 5.0 to 1.0                             1.00%             2.50%           .50%

Greater than 4.1 to 1.0 but equal to or              .75%             2.25%          .375%
 less than 5.0 to 1.0

Greater than 3.1 to 1.0 but equal to or              .50%             2.00%           .25%
 less than 4.1 to 1.0

Greater than 2.1 to 1.0 but equal to or              .25%             1.75%          .125%
 less than 3.1 to 1.0

Equal to or less than 2.1 to 1.0                       0%             1.50%          .125%
</TABLE>

                                      -2-
<PAGE>

          In the event of a Default or Event of Default hereunder, the
     Applicable Margin shall be 1.00% in the case of the Domestic Rate Margin,
     2.50% in the case of the Eurodollar Rate Margin and .50% in the case of the
     Facility Fee. Notwithstanding anything to the contrary contained herein,
     from March 29, 2001 through and including August 16, 2001, the Eurodollar
     Rate Margin shall be 2.75%.

          (b)  Section 1.2 of the Loan Agreement is hereby amended by amending
the following defined term in its entirety as follows:

               "Maximum European Loan Amount" shall mean $9,000,000.
                ----------------------------

          (c)  Section 1.2 of the Loan Agreement is hereby amended by amending
the following defined term in its entirety as follows:

               "Maximum U.S. Loan Amount" shall mean $41,000,000.
                ------------------------

          (d)   Section 2.1(a) of the Loan Agreement is hereby amended in its
entirety to read as follows:

          "(a)  U.S. Borrowing Base.  Subject to the terms and conditions set
                -------------------
     forth in this Agreement, each Lender, severally and not jointly, agrees to
     make U.S. Revolving Advances to U.S. Borrowers in accordance with the
     procedures provided for herein in an aggregate amount outstanding at any
     time not greater than such Lender's Commitment Percentage of the U.S.
     Borrowing Base (as defined below) minus (1) the undrawn or unreimbursed
                                       -----
     amount of outstanding U.S. Letters of Credit and (2) Swingline Loans
     outstanding.  For purposes hereof, "U.S. Borrowing Base" shall mean the
     lesser of (x) the Maximum U.S. Loan Amount or (y) the sum of:

               (i)   (x) from April 17, 2001 through and including August 16,
          2001, 90% and (y) from August 17, 2001 and thereafter, 85%, subject to
          the provisions of Section 2.1(b) hereof ("U.S. Receivables Advance
          Rate"), of Eligible Receivables of U.S. Borrowers, plus
                                                             ----

               (ii)  the lesser of (x) (A) from April 17, 2001 through and
          including August 16, 2001, $21,000,000 and (B) from August 17, 2001
          and thereafter, $18,000,000 or (y) (A) from April 17, 2001 through and
          including August 16, 2001, up to 70% and (B) from August 17, 2001 and
          thereafter, up to 60%, subject to the provisions of Section 2.1(b)
          hereof ("U.S. Inventory Advance Rate"), of Eligible Inventory of U.S.
          Borrowers (the U.S. Receivables Advance Rate and the U.S. Inventory
          Advance Rate shall be referred to, collectively, as the "U.S. Advance
          Rates"), plus
                   ----

               (iii) from March 29, 2001 through and including April 16, 2001,
          $6,000,000 less advances made pursuant to Section 2.1A(a)(iii) below,
          minus
          -----

                                      -3-
<PAGE>

               (iv)  such reserves as Agent may, in a commercially reasonable
          manner, reasonably deem proper and necessary.

          The U.S. Revolving Advances shall otherwise be evidenced by a U.S.
     Revolving Credit Note in the form attached hereto as Exhibit 2.1."
                                                          -----------

          (e)  Section 2.1A(a) of the Loan Agreement is hereby amended in its
entirety to read as follows:

          "(a) European Borrowing Base.  Subject to the terms and conditions
               -----------------------
     set forth in this Agreement, each Lender, severally and not jointly, agrees
     to make European Advances to European Borrowers in accordance with the
     procedures provided for herein in an aggregate amount outstanding at any
     time not greater than such Lender's Commitment Percentage of the European
     Borrowing Base (as defined below) minus the undrawn or unreimbursed amount
                                       -----
     of outstanding European Letters of Credit.  For purposes hereof, "European
     Borrowing Base" shall mean the lesser of (x) the Maximum European Loan
     Amount or (y) the sum of:

               (i)   (x) from April 17, 2001 through and including August 16,
          2001, 90% and (y) from August 17, 2001 and thereafter, 85%, subject to
          the provisions of Section 2.1A(b) hereof ("European Receivables
          Advance Rate"), of Eligible Receivables of European Borrowers, plus
                                                                         ----

               (ii)  the lesser of (x) $5,000,000 or (y) (A) from April 17, 2001
          through and including August 16, 2001, up to 70% and (B) from August
          17, 2001 and thereafter, up to 60%, subject to the provisions of
          Section 2.1A(b) hereof ("European Inventory Advance Rate"), of
          Eligible Inventory of European Borrowers (the European Receivables
          Advance Rate and the European Inventory Advance Rate shall be referred
          to, collectively, as the "European Advance Rates"), plus
                                                              ----

               (iii) from March 29, 2001 through and including April 16, 2001,
          $6,000,000 less advances made pursuant to Section 2.1(a)(iii) above,

          minus
          -----

               (iv) such reserves as Agent may, in a commercially reasonable
          manner, reasonably deem proper and necessary.

          The European Revolving Advances shall otherwise be evidenced by a
     European Revolving Note in the form attached hereto as Exhibit 2.1A."
                                                            ------------

     (f)  Section 6.9 of the Loan Agreement is hereby amended to read in its
entirety as follows:

               "6.9 Net Income.  Achieve Net Income (excluding non-cash
                    ----------
          extraordinary items and including the Chevron settlement amount
          referenced

                                      -4-
<PAGE>

          in Footnote 3 to the Company's audited financial statements for the
          year ended December 31, 2000) of (x) not less than a negative
          $1,000,000 for the fiscal year 2000, and (y) thereafter, at least $1
          in each fiscal year, for Radnor on a Consolidated Basis."

               (g)  The Maximum Ratio of Funded Indebtedness to EBITDA set forth
in Section 6.10 of the Loan Agreement is hereby amended as follows:

                                                    Maximum Ratio of
               Period                        Funded Indebtedness to EBITDA
               ------                        -----------------------------
          3/31/2000 through 12/31/2000               6.00 to 1.00
          3/31/2001                                  6.50 to 1.00
          6/30/01                                    6.30 to 1.00
          9/30/2001                                  5.75 to 1.00
          12/31/2001 through 6/30/2002               5.00 to 1.00
          9/30/2002 through 12/31/2002               4.50 to 1.00
          3/31/2003 and thereafter                   4.00 to 1.00

          (h)  The Capital Expenditure limits set forth in Section 7.6 of the
Loan Agreement are hereby amended for the following periods as follows:

               Fiscal Year Ended                        Amount
               -----------------                        ------
               12-31-00                              $15,500,000

          (i)  A new Section 6.16 is hereby added immediately following Section
6.15 to read as follows:

     "Section 6.16  Additional Collateral Documents

     Each Borrower shall, and shall cause its Subsidiaries and its Affiliates
to, at its expense, enter into any additional security, guaranty or other
collateral agreements, as may be requested by the Lenders, which agreements
shall be in form and substance satisfactory to the Lenders in their sole
discretion."

     3.   Conditions of Effectiveness.  This Amendment shall become effective
          ---------------------------
upon satisfaction of the following conditions precedent:

          (a)  the receipt by the Agent, on behalf of the Lenders, of four (4)
copies of this Amendment executed by the Borrowers and the Required Lenders; and

          (b)  the Borrowers shall have paid the amendment fee to each Lender
party to this Amendment.

     4.   Representations and Warranties.  Each of the Borrowers hereby
          ------------------------------
represents and warrants as follows:

                                      -5-
<PAGE>

          (a)  It has taken all necessary action to authorize the execution,
delivery and performance of this Amendment;

          (b)  This Amendment has been duly executed and delivered by such
Borrower and constitutes such Borrower's legal, valid and binding obligation,
enforceable in accordance with its terms.

          (c)  No consent, approval, authorization or order of, or filing,
registration or qualification with, any court or governmental authority or third
party is required in connection with the execution, delivery or performance by
such Borrower of this Amendment.

          (d)  The representations and warranties of the Borrowers set forth in
the Loan Agreement are true and correct as of the date hereof (except those that
expressly relate to an earlier date) and all provisions of the Loan Agreement
and the Other Documents, except as amended hereby, are in full force and effect.

          (e)  No Event of Default or Default has occurred and is continuing or
would exist after giving effect to this Amendment.

          (f)  Such Borrower has no defenses, counterclaims or offsets with
respect to the Loan Agreement and its performance of its obligations thereunder,
or if such Borrower has any such defenses, claims, counterclaims or offsets to
the Loan Agreement or the Other Documents or any transaction related to the Loan
Agreement or the Other Documents, the same are hereby waived, relinquished and
released in consideration of the Required Lender's execution and delivery of
this Amendment.

     5.   Effect on the Loan Agreement.
          ----------------------------

          (a)  Upon the effectiveness of this Amendment, each reference in the
Loan Agreement to "this Agreement," "hereunder," "hereof," "herein" or words of
like import shall mean and be a reference to the Loan Agreement, as amended
hereby.  The Other Documents, now or hereafter executed and delivered pursuant
to the terms of the Loan Agreement are hereby amended so that any reference to
the Loan Agreement shall mean a reference to the Loan Agreement as amended
hereby.

          (b)  Except as specifically amended herein, the Loan Agreement and the
Other Documents, now or hereafter executed and delivered pursuant to the terms
of the Loan Agreement, shall remain in full force and effect, and are hereby
ratified and confirmed.

          (c)  The execution, delivery and effectiveness of this Amendment shall
not operate as a waiver of any right, power or remedy of any Lender or the
Agent, nor constitute a waiver of any provision of the Loan Agreement or the
Other Documents executed and/or delivered under or in connection therewith.

                                      -6-
<PAGE>

     6.   Governing Law.  This Amendment shall be binding upon and inure to the
          -------------
benefit of the parties hereto and their respective successors and assigns and
shall be governed by and construed in accordance with the laws of the State of
New York.

     7.   Headings.  Section headings in this Amendment are included herein for
          --------
convenience of reference only and shall not constitute a part of this Amendment
for any other purpose.

     8.   Counterparts, Telecopied Signatures.  This Amendment may be executed
          -----------------------------------
in any number of and by different parties hereto, on separate counterparts, all
of which when so executed shall be deemed an original, but all such counterparts
shall constitute one and the same agreement.  Any signature delivered by a party
by facsimile transmission shall be deemed to be an original signature hereto.

     9.   Expenses.  Each of the Borrowers, jointly and severally, agrees to pay
          --------
all reasonable costs and expenses incurred in connection with the negotiation,
execution and delivery of this Amendment, including the reasonable fees and
expenses of the Agent's legal counsel.

     10.  ENTIRETY.  THIS AMENDMENT, THE LOAN AGREEMENT AND THE OTHER DOCUMENTS
          --------
EMBODY THE ENTIRE AGREEMENT BETWEEN THE PARTIES AND SUPERSEDE ALL PRIOR
AGREEMENTS AND UNDERSTANDINGS, IF ANY, RELATING TO THE SUBJECT MATTER HEREOF.
THIS AMENDMENT, THE LOAN AGREEMENT AND THE OTHER DOCUMENTS REPRESENT THE FINAL
AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES.

                 [Remainder of Page Left Intentionally Blank]

                                      -7-
<PAGE>

     IN WITNESS WHEREOF, this Amendment has been duly executed as of the day and
year first written above.

U.S. BORROWERS:               WINCUP HOLDINGS, INC.

                              By:______________________________

                              RADNOR CHEMICAL CORPORATION

                              By:______________________________

                              STYROCHEM U.S., LTD.
                              By its general partner, StyroChem GP, L.L.C.
                              By its sole member, Radnor Chemical Corporation

                              By:______________________________

                              RADNOR HOLDINGS CORPORATION

                              By:______________________________

                              RADNOR DELAWARE, INC.

                              By:______________________________

                              STYROCHEM DELAWARE, INC.

                              By:______________________________

<PAGE>

                              WINCUP TEXAS, LTD.
                              By its general partner, WinCup GP, L.L.C.
                              By its sole member WinCup Holdings, Inc.

                              By:______________________________

EUROPEAN BORROWERS:           STYROCHEM EUROPE (THE NETHERLANDS) B.V.

                              By:______________________________

                              STYROCHEM FINLAND OY

                              By:______________________________

                              THERMISOL DENMARK A/S

                              By:______________________________

<PAGE>

                              THERMISOL SWEDEN AB

                              By:______________________________

                              THERMISOL FINLAND OY.

                              By:______________________________

AGENT AND LENDERS:            BANK OF AMERICA, N.A.
                              as Agent and a Lender

                              By:______________________________
                              Name:____________________________
                              Title:___________________________

                              FIRST UNION NATIONAL BANK,
                              as a Lender

                              By:______________________________
                              Name:____________________________
                              Title:___________________________

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