<PAGE>
                                                                  Exhibit 10(z)


                                                                   LETTER OF   
OUR CREDIT NO.      ISSUE DATE           EXPIRY DATE             CREDIT AMOUNT
--------------      ----------           -----------             -------------
SM406777         October 29, 1998       March 31, 2001           $7,641,781.00

BENEFICIARY                                     APPLICANT
-----------                                     ---------
First Union National Bank, as trustee           Central CPVC Corporation
123 South Broad Street                          451 North Cannon Avenue
Philadelphia, Pennsylvania 19109                Lansdale, Pennsylvania 19446

Attention: Corporate Trust Administration

Dear Beneficiary:

         At the request, on the instructions and for the account of our
customer, Central CPVC Corporation (the "Applicant"), with a business address at
451 North Cannon Avenue, Lansdale, Pennsylvania 19426, we (the "Bank") hereby
establish our Irrevocable Letter of Credit No. SM406777 (the "Letter of Credit")
in your favor, as Trustee under the Trust Indenture, dated as of October 1, 1998
(the "Indenture"), between The Industrial Development Board of the City of
Huntsville (the "Board") and you pursuant to which $7,500,000 in aggregate
principal amount of the Board's Tax-Exempt Variable Rate Demand/Fixed Rate
Refunding Revenue Bonds (Central CPVC Corporation Project), Series of 1998 (the
"Bonds") are being issued. This Letter of Credit is irrevocable and issued with
respect to the Bonds.

         This Irrevocable Letter of Credit is issued in the aggregate initial
amount of Seven Million Six Hundred Forty-One Thousand Seven Hundred Eighty-One
Dollars ($7,641,781) (such amount, as reduced and reinstated from time to time
in accordance with the provisions hereof, the "Stated Amount") of which (i) an
amount not exceeding Seven Million Five Hundred Thousand Dollars ($7,500,000)
(as reduced and reinstated from time to time in accordance with the terms
hereof, the "Principal Component"), may be drawn upon with respect to payment of
the unpaid principal amount or the portion of Purchase Price corresponding to
principal of the Bonds and (ii) an amount not exceeding One Hundred Forty-One
Thousand Seven Hundred Eighty-One Dollars ($ 141,781) (representing 46 days of
interest computed at the rate of 15% per annum as reduced and reinstated from
time to time in accordance with the terms hereof, the "Interest Component") may
be drawn upon with respect to payment of unpaid accrued interest, or the portion
of Purchase Price corresponding to interest, on the Bonds on or prior to their
stated maturity date, effective immediately and expiring on March 31, 2001 (the
"Expiration Date").

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First Union National Bank
October 29, 1998
Page 2


         Subject to the foregoing and the further provisions of this Letter of
Credit, a demand for payment may be made by you under this Letter of Credit
against your sight draft(s) drawn on us, signed by an Authorized Officer stating
on its face the clause, "Drawn under First Union National Bank Irrevocable
Letter of Credit No. SM406777" and accompanied by: (A) if the drawing is being
made with respect to the payment of the portion of the Purchase Price of the
Bonds delivered to the Tender Agent (as defined in the Indenture) pursuant to
Sections 5.01, 5.03 or 5.04 of the Indenture, corresponding to the principal
thereof (an "A Drawing"), receipt by us of your written certificate in the form
of Exhibit A attached hereto appropriately completed and signed by an Authorized
Officer; (B) if the drawing is being made with respect to the payment of
principal of the Bonds upon maturity or as a result of acceleration or
redemption of the Bonds (a "B Drawing"), receipt by us of your written
certificate in the form of Exhibit B attached hereto, appropriately completed
and signed by an Authorized Officer, and (C) if the drawing is being made with
respect to the payment of interest, or the portion of Purchase Price
corresponding to interest, on the Bonds (a "C Drawing"), receipt by us of your
written certificate in the form of Exhibit C attached hereto, appropriately
completed and signed by an Authorized Officer. Presentation of such sight
draft(s) and certificate(s) shall be made by writing (including telecopier) at
our office located at First Union National Bank, 1345 Chestnut Street, 9th
Floor, Philadelphia, Pennsylvania 19107, Attention: Letter of Credit Department,
telephone number: (215) 973-8157, telecopier number: (215) 786-8803, or at any
other office which may be designated by us by written notice delivered to you.
All payments made by the Bank shall be made with its own funds.

         Demands for payment may be made by you under this Letter of Credit on
or prior to the expiration hereof at any time during our business hours on a
Business Day at the address at which your sight draft(s) is(are) to be presented
in accordance with the terms hereof. As used herein the term "Business Day"
means any day other than (i) a Saturday or Sunday, (ii) a legal holiday or any
other day on which banking institutions in the State of New York, the
Commonwealth of Pennsylvania, the City of New York, the city in which the
office of the Trustee and the Tender Agent administering the Indenture is
located, the city in which the principal office of the Bank is located, are
authorized or required by law to close, or (iii) a day on which the New York
Stock Exchange is closed. If your sight draft accompanied by documents
conforming to the terms and conditions of this Letter of Credit is made by you
at or prior to 12:00 noon (Eastern Time) on a Business Day, such draft will be
honored by us by 12:00 noon (Eastern Time) on the next succeeding Business Day.
If your sight draft accompanied by documents conforming to the terms and
conditions of this Letter of Credit is made by you after 12:00 noon (Eastern
Time) on a Business Day, such draft will be honored by us by 12:00 noon (Eastern
Time) on the second succeeding Business Day. Payment of any draft indicating a

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First Union National Bank
October 29, 1998
Page 3


payment date which is not a Business Day as defined herein will be effected the
next succeeding Business Day. If a demand for payment made by you hereunder does
not, in any instance, conform to the terms and conditions of this Letter of
Credit, we shall give you prompt notice that the purported negotiation was not
effected in accordance with the terms and conditions of this Letter of Credit,
stating the reasons therefor and that we are holding any documents at your
disposal or are returning the same to you, as we may elect. Upon being notified
that the purported negotiation was not effected in conformity with this Letter
of Credit, you may attempt to correct any such nonconforming demand for payment
if, and to the extent that, you are entitled (without regard to the provisions
of this sentence) and able to do so.

         Demands for payment hereunder honored by us shall not, in the
aggregate, exceed the Stated Amount, as the Stated Amount may have been reduced
by us or reinstated by us as provided below. Subject to the reinstatement
effected in accordance with the terms hereof, each "A Drawing" and each "B
Drawing" honored by the Bank hereunder shall pro tanto reduce the Principal
Component and each "C Drawing" honored by the Bank hereunder shall pro tanto
reduce the Interest Component; any such reduction shall result in a
corresponding reduction in the Stated Amount, it being understood that after the
effectiveness of any such reduction you shall no longer have any right to make a
drawing hereunder in respect of the amount of such principal and/or interest on
the Bonds or the payment of Purchase Price corresponding thereto.

         Upon reimbursement to us or Congress Financial Corporation
("Congress"), as Congress so directs, from the proceeds of a remarketing of
Bonds purchased with the proceeds of an "A Drawing" hereunder, of all amounts
paid by us pursuant to an "A Drawing" hereunder, the Principal Component shall
be reinstated automatically by the amount of such reimbursement. In addition, if
you shall not have received, within ten calendar days after any payment in
respect of a "C Drawing", written notice by tested telex from us that Congress
has determined not to reinstate the Letter of Credit because either (i) the
Company has failed to reimburse the Bank or Congress for the amount of such
payment, together with interest thereon, or (ii) there is presently existing an
Event of Default under and as defined in the Loan and Security Agreement dated
September 18, 1998 (the "Loan Agreement") by and between the Applicant, certain
affiliates of Applicant and Congress, the Interest Component shall be reinstated
automatically, as of the opening of business on the tenth calendar day
following such payment, by the amount of such "C Drawing"; provided, however,
that in the event such "C Drawing" shall be submitted in respect of the payment
of the portion of the Purchase Price corresponding to interest on the Bonds,
upon reimbursement to us or Congress, as Congress so directs, from the proceeds
of a remarketing of Bonds of all amounts paid by us pursuant to a "C Drawing"
hereunder, the Interest Component shall be reinstated automatically by the
amount of such reimbursement;


<PAGE>


First Union National Bank
October 29, 1998
Page 4


provided further, that in no event shall the Interest Component be reinstated to
an amount in excess of 46 days' interest (such amount computed as set forth in
the third succeeding paragraph of this Letter of Credit) on the sum of the then
applicable Principal Component plus the aggregate principal amount of any
Pledged Bonds. Upon presentation to us by the Trustee of the Reduction
Certificate attached hereto as Exhibit D, we will automatically reduce the
Stated Amount of this Letter of Credit.

         Only you as Trustee may make a drawing under this Letter of Credit.
Upon the payment to you, to your designee or to your order of the amount
specified in a sight draft drawn, we shall not thereafter be obligated to make
any further payments under this Letter of Credit with respect to such sight
draft to you or any other person who may have made to you or makes to you a
demand for payment of principal of, Purchase Price of, or interest on, any
Bond. By paying to you an amount demanded in accordance herewith, we make no
representation as to the correctness of the amount demanded.

         Payments made by us hereunder will be made to you in immediately
available funds and out of our funds, and not, directly or indirectly, out of
funds or other assets of the Applicants.

         This Letter of Credit applies only to the payment of principal or the
portion of Purchase Price of the Bonds corresponding to principal, provided,
that any of the Bonds pledged to the Bank will not be entitled to the payment of
principal with funds drawn hereunder until the principal amount of all other
Bonds has been paid, and to pay up to $ 141,781 which is 46 days' interest
accruing on the Bonds (computed at a rate of 15% per annum), from the Issue Date
through the Expiration Date (computed on the basis of a 365- or 366-day year,
actual days elapsed, notwithstanding the actual rate borne from time to time by
the Bonds) and does not apply to any interest that may accrue thereon or any
principal, or other amounts which may be payable with respect to the Bonds
subsequent to the expiration of this Letter of Credit.

         This Letter of Credit shall automatically terminate and be delivered to
the Bank for cancellation, at 4 p.m. (Eastern Time) on the date which is the
earliest of (i) upon receipt of your certificate in the form of Exhibit E signed
by an Authorized Officer and the honoring by us of the final drawing available
to be made hereunder, (ii) five calendar days after the date upon which we
receive your certificate in the form of Exhibit E signed by an Authorized
Officer with respect to either (a) receipt of a Substitute Letter of Credit or
(b) conversion of the Bonds to a fixed rate of interest, (iii) upon receipt of
your certificate in the form of Exhibit E signed by an Authorized Officer to the
effect that no Bonds remain outstanding under the Indenture, together with the
Letter of Credit and (iv) March 31, 2001, the stated Expiration Date. This
Letter of Credit shall


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First Union National Bank
October 29, 1998
Page 5


be promptly surrendered to us by you upon such termination.

         Communications with respect to this Letter of Credit shall be in
writing and shall be addressed to us at First Union National Bank, 1345 Chestnut
Street, 9th Floor, Philadelphia Pennsylvania 19107, Attention: Letter of Credit
Department, specifically referring thereon to this Letter of Credit by number.

         This Letter of Credit is transferable in its entirety (but not in part)
to any transferee who has succeeded you as Trustee under the Indenture. We agree
to issue a substitute Letter of Credit to any such successor trustee (and to
successively replace any such substitute letter of credit) upon the return to us
for cancellation of the original of the Letter of Credit to be replaced,
accompanied by a request relating to such Letter of Credit, which (i) shall be
substantially in the form of Exhibit F attached hereto with the blanks
appropriately completed, (ii) shall be signed by an Authorized Officer, (iii)
shall specifically refer to the letter of credit number as the number of the
letter of credit to be replaced and (iv) shall state the name and address of the
successor trustee. 

         As used herein (a) "Authorized Officer" shall mean any person signing
as one of your Vice Presidents, Assistant Vice Presidents, Trust Officers or
Assistant Trust Officers and (b) "Purchase Price" shall mean the principal
amount of, together with accrued interest on, any Bonds to be purchased in
accordance with Sections 5.01, 5.03 or 5.04 of the Indenture. Other capitalized
terms used herein but not defined herein shall have the same meanings as in the
Indenture or in the Loan Agreement.

         This Letter of Credit sets forth in full our undertaking, and such
undertaking shall not in any way be modified, amended, amplified or limited by
reference to any document, instrument or agreement referred to herein
(including, without limitation, the Bonds), except only the certificate(s) and
sight draft(s) referred to herein; and any such reference shall not be deemed to
incorporate herein by reference any document, instrument or agreement except for
such certificate(s) and such sight draft(s).

<PAGE>

First Union National Bank
October 29, 1998
Page 6


         This Letter of Credit is subject to the Uniform Customs and Practice
for Documentary Credits (1993 Revision), International Chamber of Commerce,
Publication No. 500 (the "Uniform Customs"). This Letter of Credit shall be
deemed to be made under the laws of the Commonwealth of Pennsylvania and shall,
as to matters not governed by the Uniform Customs, be governed by and construed
in accordance with the laws of the Commonwealth of Pennsylvania. 

                                       Very truly yours, 

                                       FIRST UNION NATIONAL BANK 

                                       /s/ Richard Fortina
                                       -------------------------
                                       AUTHORIZED SIGNATURE 

<PAGE>

                                                                      EXHIBIT A
 
                           CERTIFICATE FOR "A DRAWING"
                (Draws with respect to payment of Purchase Price
             of the Bonds pursuant to Mandatory and Optional Tenders
                                  of the Bonds)

                                                                         [Date] 

First Union National Bank 
1345 Chestnut Street, 9th Floor 
Philadelphia, Pennsylvania 19107
Attention: Letter of Credit Department 

Re: Irrevocable Letter of Credit No. SM406777
    ------------------------------------------ 

         The undersigned, a duly authorized officer of First Union National Bank
(the "Trustee"), hereby certifies to First Union National Bank (the "Bank") with
reference to the Bank's Irrevocable Letter of Credit No. SM406777 (the "Letter
of Credit") (any capitalized terms used herein and not defined shall have its
respective meaning as set forth in the Letter of Credit issued by the Bank in
favor of the Trustee) that:

    (1) The Trustee is the Trustee under the Indenture for the holders of the
    Bonds.

    (2) The Trustee is making a drawing under the above-referenced Letter of
    Credit in the amount of $__________ with respect to payment of the portion
    of the Purchase Price of Bonds corresponding to the principal amount
    thereof, which Bonds are to be purchased pursuant to Sections 5.01, 5.03 or
    5.04 of the Indenture.

    (3) The amount of the sight draft accompanying this certificate hereby does
    not exceed the stated amount or the amount available on the date hereof to
    be drawn under the above-referenced Letter of Credit in respect of the
    portion of the Purchase Price of Bonds corresponding to the principal amount
    thereof.

    (4) Upon receipt by the undersigned of the amount demanded hereby, (a) the
    undersigned will transfer such amount to the Tender Agent for the payment
    when due of


<PAGE>

    the principal amount owing on account of the purchase of the Bonds pursuant
    to the Indenture, (b) no portion of said amount shall be applied by the
    undersigned for any other purpose and (c) no portion of said amount shall be
    commingled with other funds held by the undersigned.

    IN WITNESS WHEREOF, the Trustee has executed and delivered this Certificate 
as of the ______ day of _____________________19__.


                                     FIRST UNION NATIONAL BANK, as trustee

                                     By:__________________________________
                                     Title:_______________________________


<PAGE>

                                                                       EXHIBIT B
 
                          CERTIFICATE FOR "B DRAWING"
         (Draws with respect to payment of principal at maturity, upon
                   acceleration or upon partial redemption or
                              redemption in whole)

                                                                          [Date]

First Union National Bank
1345 Chestnut Street, 9th Floor
Philadelphia, Pennsylvania 19107
Attention: Letter of Credit Department

Re: Irrevocable Letter of Credit No. SM406777
    -----------------------------------------

         The undersigned, a duly authorized officer of First Union National Bank
(the "Trustee"), hereby certifies to First Union National Bank (the "Bank") with
reference to the Bank's Irrevocable Letter of Credit No. SM406777 (the "Letter
of Credit") (any capitalized terms used herein and not defined shall have its
respective meaning as set forth in the Letter of Credit issued by the Bank in
favor of the Trustee) that:

    (1) The Trustee is the Trustee under the Indenture for the holders of the
    Bonds.

    (2) The Trustee is making a drawing under the above-referenced Letter of
    Credit in the amount of $________ with respect to payment of the principal
    of the Bonds, which amount has, or will, within five business days, become
    due and payable pursuant to the Indenture, upon maturity or as a result of
    acceleration or redemption of the Bonds.

    (3) The amount of the sight draft accompanying this certificate hereby does
    not exceed the stated amount or the amount available on the date hereof to
    be drawn under the above-referenced Letter of Credit in respect of the
    principal of the Bonds.

    (4) Upon receipt by the undersigned of the amount demanded hereby, (a) the
    undersigned will apply the same directly to the payment when due of the
    principal amount owing on account of the maturity, redemption or
    acceleration of the Bonds

<PAGE>

    pursuant to the Indenture, (b) no portion of said amount shall be applied by
    the undersigned for any other purpose and (c) no portion of said amount
    shall be commingled with other funds held by the undersigned.

    IN WITNESS WHEREOF, the Trustee has executed and delivered this Certificate
as of the _____ day of __________________ 19__.


                                     FIRST UNION NATIONAL BANK, as trustee

                                     By:__________________________________
                                     Title:_______________________________

<PAGE>


                                                                      EXHIBIT C
 
                          CERTIFICATE FOR "C DRAWING"
                       (Draws with respect to payment of
                        accrued interest upon the Bonds)

                                                                         (Date]

First Union National Bank
1345 Chestnut Street, 9th Floor
Philadelphia, Pennsylvania 19107
Attention: Letter of Credit Department

Re: Irrevocable Letter of Credit No. SM406777
    -----------------------------------------

         The undersigned, a duly authorized officer of First Union National Bank
(the "Trustee"), hereby certifies to First Union National Bank (the "Bank") with
reference to the Bank's Irrevocable Letter of Credit No. SM406777 (the "Letter
of Credit") (any capitalized terms used herein and not defined shall have its
respective meaning as set forth in the Letter of Credit issued by the Bank in
favor of the Trustee) that:

    (1) The Trustee is the Trustee under the Indenture for the holders of the
    Bonds.

    (2) The Trustee is making a drawing under the above-referenced Letter of
    Credit in the amount of $___________ with respect to payment of [the portion
    of the Purchase Price of $_____________ in principal amount of the Bonds
    corresponding to the accrued interest thereon, which Bonds are to be
    purchased pursuant to Sections 5.01, 5.03 or 5.04 of the Indenture] or
    [interest on the Bonds, which amount has accrued and become due and payable
    pursuant to the Indenture, upon a stated Interest Payment Date or as a
    result of acceleration or redemption of the Bonds].

    (3) The amount of the sight draft accompanying this certificate hereby does
    not exceed $____________ (which represents no more than 46 days' interest
    accrued on the Bonds), the amount available on the date hereof to be drawn
    under the above-referenced Letter of Credit in respect of unpaid accrued
    interest on the Bonds or the portion of the Purchase Price corresponding to
    interest on the Bonds.

<PAGE>


    (4) Upon receipt by the undersigned of the amount demanded hereby, (a) the
    undersigned will [apply the same directly to the payment when due of the
    interest owing on account of the Bonds pursuant to the Indenture] or
    [transfer such amount to the Tender Agent for the payment of the portion of
    the Purchase Price of Bonds pursuant to Sections 5.01, 5.03 or 5.04 of the
    Indenture corresponding to accrued interest thereon], (b) no portion of said
    amount shall be applied by the undersigned for any other purpose and (c) no
    portion of said amount shall be commingled with other funds held by the
    undersigned. 

    IN WITNESS WHEREOF, the Trustee has executed and delivered this Certificate 
as of the _______ day of 19__. 

                                      FIRST UNION NATIONAL BANK, as trustee

                                      By:_______________________________ 
                                      Title:____________________________

<PAGE>

                                                      First Union National Bank 
                                                   Irrevocable Letter of Credit 
                                                                   No. SM406777

                                   EXHIBIT D

                             REDUCTION CERTIFICATE

         The undersigned, a duly authorized officer of First Union National Bank
(the "Trustee"), hereby certifies as follows to First Union National Bank as
issuer of the above-referenced letter of credit (the "Letter of Credit").

         1. All terms defined in the Letter of Credit are used herein with the
same meanings. 

         2. The Trustee is the Trustee under the Indenture.

         3. The Trustee hereby notifies you that on or prior to the date hereof
the Bonds in a principal amount of ______________ Dollars ($__________ ) have
been redeemed or defeased, and are deemed paid, pursuant to the Indenture.

         4. The Trustee hereby consents to a reduction in the Stated Amount by
______________ Dollars ($____________), representing the sum of the aggregate
principal amount of the Bonds referred to in the preceding paragraph hereof and
interest thereon in the amount of _____________ Dollars ($__________).

Dated:_____________                    FIRST UNION NATIONAL BANK, as trustee

                                       By:__________________________________ 
                                       Title:_______________________________

<PAGE>

                                                       First Union National Bank
                                                    Irrevocable Letter of Credit
                                                                    No. SM406777
                                   EXHIBIT E

                            TERMINATION CERTIFICATE

         The undersigned, a duly authorized officer of First Union National Bank
(the "Trustee"), hereby certifies as follows to First Union National Bank as
issuer of the above-referenced letter of credit (the "Letter of Credit").

         1. All terms defined in the Letter of Credit are used herein with the
same meanings.

         2. The Trustee is the Trustee under the Indenture.

         3. The Trustee hereby requests termination of the Letter of Credit
submitted herewith for the following reason [state one of the following]:

            (a) The draft or demand accompanying this Certificate is the final
draft or demand to be drawn under the Letter of Credit and, upon the honoring of
such draft or demand, the Trustee will surrender the Letter of Credit to the
Bank for cancellation;

            (b) The conditions precedent to the acceptance of a Substitute
Letter of Credit have been satisfied and the Trustee has accepted the Substitute
Letter of Credit; or

            (c) The Bonds have been converted to a fixed rate of interest in
accordance with the Indenture; or

            (d) No Bonds remain Outstanding (as defined in the Indenture).

Dated:______________                    FIRST UNION NATIONAL BANK, as trustee

                                        By:__________________________________ 
                                        Title:_______________________________

<PAGE>

                                   EXHIBIT F

                              TRANSFER CERTIFICATE

                                     [Date]

First Union National Bank
1345 Chestnut Street, 9th Floor
Philadelphia, Pennsylvania 19107
Attention: Letter of Credit Department

Re: First Union Irrevocable Letter of Credit No. SLM406777
    ------------------------------------------------------

Gentlemen:

         Reference is made to (i) the above-referenced letter of credit (the
"Old Letter of Credit") and (ii) the Trust Indenture dated as of October 1, 1998
(the "Indenture") between The Industrial Development Board of the City of
Huntsville and us.

         [Name and address of successor trustee] (the "Successor Trustee") has
been properly appointed and qualified as successor trustee under the terms of
Article IX of the Indenture. You are hereby requested to issue, in accordance
with the terms of the Old Letter of Credit, a new letter of credit to the
Successor Trustee having the same terms and providing for the same Stated Amount
then applicable under the Old Letter of Credit.

         We submit herewith for cancellation the original of the Old Letter of
Credit.

         The individual signing below on our behalf hereby represents that he or
she is duly authorized to so sign on our behalf.

                                    Very truly yours,

                                    FIRST UNION NATIONAL BANK, as trustee

                                    By:__________________________________ 
                                    Title:_______________________________