**2. Classification of polymers**

The word polymer derived from Greek has been split into two meaningful words: (1) poly means many, and (2) meros or mers means units or parts. More specifically monomer is the smallest repeating unit for the development of polymer. Simply polymers are made up of monomers. The word monomer is also derived

**141**

**Table 1.**

**S. no.**

6 NIPAM

*structures in* **Figure 1a–j***.*

(isopropylacrylamide)

*Polymer Properties: Functionalization and Surface Modified Nanoparticles*

from the Greek. Mono means one or single and mer means part/s. As reported in **Table 1**, there are varieties of polymers classified based on their biodegradability, biocompatibility, thermal stability, pH-responsive nature, environmental responsive nature, etc. Based on occurrence these are again categorized into three types: (1) natural polymers, for example, starch, chitin, cellulose, etc., (2) synthetic polymers, for example, polystyrene (PS), polyurethane (PU), polyvinyl chloride (PVC), and (3) semisynthetic polymers, for example, cellulose nitrate, guncotton, cellulose acetate, etc. Absorbable synthetic polymers include polyvinyl alcohol (PVA), polylactic acid (PLA), polycaprolactone (PCL), and polyglycolic acid (PGA), and these are homopolymers. The heteropolymers include polytrimethylene carbonate (PTMC), polyetherimide (PEI), polydioxanone (PDO), polylactide-co-glycolide (PLGA), and the combination of block copolymers like and poly-glycolide-co-trimethylene carbonate (PGTMC) which are best examples for heterogeneous polymers. Apart from these polymers, there are pH-sensitive polymers like poly-L-lysine which is positively charged at lower pH conditions [22, 23]. Liposome and poly-histidine are the systems with pH sensitivity, and this can be easily interacted with negatively charged particles or membranes to promote fusogenic properties. Furthermore, some hydrogel-based nanoparticles show unique characteristics toward various biomedical as well as industrial applications. Liposomal and hydrogel based systems has tendency towards pH-sensitivity and it is a characteristic property to tune-up their morphology for many therapeutic applications. For example, PLGA, MeO-PEG-NH2, and PAMAM-based nanoparticles show pH-dependent destabilization and thus are used for cytoplasmic experiments because of its ease of permeability through the membrane to deliver nanomedicines and nanoparticles [9, 10, 22, 23]. The NIPAM/pNIPAM (N-isopropyl acrylamide/ (poly-N-isopropyl acrylamide)) is the best example for the thermal sensitive polymer which shows lower critical solution temperature (LCST) or cloud point at ~32°C **Table 1**. Because of the thermal behavior, it is termed as magic or smart polymer and used for various medical and industrial usages. However, these polymers are mainly prepared based on two polymerizations reactions such as (1) addition

polymerization and (2) condensation polymerization methods [24, 25].

**formula**

 PVC (polyvinyl chloride) C2H3Cl (C2H3Cl)n **Figure 1a** [11, 12] PVA (polyvinyl alcohol) C2H4O (C2H4O)n **Figure 1b** [12, 13] PE (polyethylene) C2H4 (C2H4)n **Figure 1c** [12, 14] PS (polystyrene) C8H8 (C8H8)n **Figure 1d** [14, 15] PP (polypropylene) C3H6 (C3H6)n **Figure 1e** [15, 16]

 PTFE (Teflon) C2F4 (C2F4)n **Figure 1g** [17, 18] PCL (polycaprolactone) C6H10O2 (C6H10O2)n **Figure 1h** [18, 19] PEI (polyetherimide) C37H24O6N2 (C37H24O6N2)n **Figure 1i** [19, 20] PSU (polysulfone) C27H22O4S (C27H22O4S)n **Figure 1j** [20, 21]

*Show the different types of polymers with their monomer units and their chemical formula followed by the* 

*Here, "n" represents the number of monomer units involved in the synthesis of the polymers.*

**Polymer formula**

C6H11NO (C6H11NO)n **Figure 1f** [16, 17]

**Polymer structure** **Ref.**

**Name of the polymer Monomer** 

*DOI: http://dx.doi.org/10.5772/intechopen.84424*
