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The glass transition temperature Tg of nylon 6 decreases monotonically toward a finite value Tgl upon increase of the moisture content. The mechanism of this decrease entails the reversible replacement of intercaternary hydrogen bonds in the accessible regions of the polyamide. The limiting glass transition temperature Tgl is approached when the moisture content approaches Wl, which corresponds to the amount of water required for complete interaction with all accessible amide groups. Denoting with Tg0 the glass transition temperature of the dry polymer, the effect of water on Tg is represented by the equation, Tg = (ΔTg)0 exp{−[ln(ΔTg)0]W/τWl} + Tgl, where (ΔTg)0 = Tg0 −Tgl, and τ = W(Tgl+1)/Wl. This equation appears to be generally applicable to hydrophilic polymers, since correspondingly calculated data are also in very good agreement with experimental data for polymers such as nylon 66, poly(vinyl alcohol), and polyN‐vinylpyrrolidone. The effect of water of Young's modulus E of nylon 6 is represented by an analogous relationship, and the quantity In[(E−El)/(Tg−Tgl)] is a linear function of the moisture content.

Polymers composed of monomer units that contain n‐alkyl side chains are characterized by a monotonical decrease in the glass transition temperatures toward a critical value (Tg)c as the number of C atoms in the side chain increases toward a corresponding critical value nc. Thus the glass transition temperatures of these comblike polymers are for a given backbone chain structure directly related to the molecular weight (M) of the monomer unit. This relationship can be represented by the differential equation dTg/dM = −k′M[Tg − (Tg)c], which on integration yields Tg = (ΔTg)0 exp−[k(M2 − M 12)] + (Tg)c, where (ΔTg) = (Tg)1 − (Tg)c, and the subscript 1 refers to n = 1. Values for Tg calculated according to this relationship are in good agreement with published data on polybutadienes, polystyrenes, poly(vinyl ether)s, polyacrylates, polymethacrylates, polyitaconates, poly(phenylene ether)s, and poly(N‐maleimide)s. For these polymers the critical quantities nc and (Tg)c can be estimated rather well by the simple relationships nc = 1 + 2.8 × 10−2 (Tg)1 and (Tg)c = (Tg)1 − nc(nc − 1). The Tg(M) relationship derived appears to be applicable also to copolymers that contain monomer units with alkyl side chains.

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SynopsisThe progress of photo-and photooxidative degradation of nylon films were studied by FT-IR spectroscopy. The gases evolved from the photolysis of various nylons and their model amides were also analyzed. The formation of double bonds, changes of crystallinity, and the effect of amino and carboxyl end groups has been studied and discussed. The band shapes of the IR spectra pertaining to the carbonyl groups formed by thermal oxidation or photooxidation were found to be very similar, suggesting that the two oxidation mechanisms might be similar. The broadness of these bands indicates that the carbonyl groups may belong to more than one species. The photodegradation of nylons containing purposely inserted carbonyl groups formed -CH=CH, groups. Carbonyl groups formed during oxidation, and present either as keto groups or part of N-acylamide units make nylons susceptible to degradation reactions entailing mainly a Nonish type I1 mechanism.From ESR s t~d i e s ,~,~ kinetic studies,6 and chemical analyses,' the photolysis mechanisms were suggested to occur by degradation involving direct cleavage of the amide bond according to a Nonish Type I mechanism. Moore suggested that both Type I and Type I1 mechanisms occurred in the degradation of nylons.8Recently, Mazzocchi and Bowen studied the photolysis of N-alkylamides in solution by analyzing the products and concluded that the Type I process was predominant and the Type I1 process was quite ineffi~ient.~ They rationalized