I don't know of any undergraduate level texts that would be suitable for a freshman, unless you have already taken physics, statistics, and chemistry up through organic chemistry.
I can tell you that Fundamentals of Polymer Science by Painter and Coleman is a good introductory text, but I used it in the final year of my Chemical Engineering program. There could be better resources as well - that's just the only one I am personally familiar with.
It also depends a lot on which specific aspects of polymers you are interested in. This actually matters a lot for your second question as well. The three main branches of polymers studies are:
- Polymer chemistry
- Polymer physics
- Polymeric materials
There are sub-fields in each of these, and a lot of overlap, but essentially they focus on:
- Polymer chemistry - How are polymers made? (this would include engineering and production of polymers)
- Polymer physics - How does the behavior on a molecular level affect the macroscopic properties?
- Polymeric materials - How can we use the unique material properties of polymers to make useful stuff?
At the undergraduate level, you won't get too specific on any one of these areas, no matter which degree you choose. If you majored in chemistry, you would learn a little more about polymerization reactions. If you majored in physics (and took electives related to polymers) you might learn more about the statistical mechanics of polymers. If you majored in materials science and/or engineering, you would learn more about how we use the polymers, and less about how they are made and why they act the way they do. Chemical engineers learn a little bit of everything, but they don't get too deep into any one particular branch.
The real differences show up if you go on to graduate school or work in a particular role in industry. There, you will definitely focus more, and your degree can make more of a difference. So I would say, for your second question, major in whatever aspect interests you more - if you want to know the details about how polymers are made in a lab, then maybe chemistry is a better option. If you really like math and physics and want to understand how they relate to the behavior of polymers, then physics is good. If you are more interested in how to characterize and use polymers, then materials science/engineering is a good bet. And if you like a little bit of everything, or are interested in industrial-scale production of polymers, then chemical engineering is a good choice.
Keep in mind as well: it is hard to predict now what you will really want to do in four or more years - so if you make a choice based on which aspects of polymer science you are interested in, and then later decide that polymers are actually not what you really like, you will still be studying the "right" stuff for you.