`=>` Polymer properties are closely related to their molecular mass, size and structure.

`=>` The growth of the polymer chain during their synthesis is dependent upon the availability of the monomers in the reaction mixture.

`=>` Therefore, the polymer sample contains chains of varying lengths and hence its molecular mass is always expressed as an average.

`=>` The molecular mass of polymers can be determined by chemical and physical methods.

`=>` A large number of polymers are quite resistant to the environmental degradation processes and are thus responsible for the accumulation of polymeric solid waste materials.

`=>` These solid wastes cause acute environmental problems and remain undegraded for quite a long time.

`=>` In view of the general awareness and concern for the problems created by the polymeric solid wastes, certain new biodegradable synthetic polymers have been designed and developed.

`=>` These polymers contain functional groups similar to the functional groups present in biopolymers.

`=>` Aliphatic polyesters are one of the important classes of biodegradable polymers.

`=>` Some important examples are given below :

`=>` It is obtained by the copolymerisation of `3`-hydroxybutanoic acid and `3`-hydroxypentanoic acid.

`color{green}("Uses ") : ` PHBV is used in speciality packaging, orthopaedic devices and in controlled release of drugs.

`=>` PHBV undergoes bacterial degradation in the environment.

`color{red}(undersettext(3-Hydroxybutanoic acid)(CH_3 - overset( overset(OH)(|))CH - CH_2-COOH) + undersettext(3-Hydroxypentanoic acid)(CH_3-CH_2- overset( overset(OH)(|))CH-CH_2-COOH) → undersettext(PHBV)((- O- underset(underset(CH_3)(|))CH-CH_2 - underset(underset(O)(||))C-O-underset(underset(CH_2CH_3)(|))CH-CH_2 - underset(underset(O)(||))C-)_n))`

It is an alternating polyamide copolymer of glycine `color{red}(H_2N–CH_2–COOH)` and amino caproic acid `color{red}([H_2N (CH_2)_5 COOH])` and is biodegradable.

Besides, the polymers already discussed, some other commercially important polymers along with their structures and uses are given below in Table 15.1.